130+ Coffee Interview Questions Answers For Ii To Seven Twelvemonth Experienced Programmers
Tuesday, September 4, 2018
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Last Updated Date: 2nd March 2018
Time is changing in addition to so is Java interviews. Gone are the days, when knowing the divergence betwixt String in addition to StringBuffer tin aid yous to travel past times away through the 2nd circular of interview, questions are becoming to a greater extent than advanced in addition to interviewers are asking to a greater extent than deep questions. When I started my career, questions similar Vector vs Array and HashMap vs Hashtable were the most pop ones in addition to only memorizing them gives yous a goodness adventure to do good inwards interviews, but non anymore. Nowadays, yous volition acquire questions from the areas where non many Java programmer looks e.g. NIO, patterns, sophisticated unit of measurement testing or those which are hard to original e.g. concurrency, algorithms, information structures in addition to coding.
Since I similar to explore interview questions, I receive got got this huge listing of questions alongside me, which contains lots in addition to lots of questions on unlike topics. I receive got been preparing this MEGA listing for quite some fourth dimension in addition to at nowadays It's cook to portion alongside yous guys.
It contains interview questions non solely from classic topics similar threads, collections, equals in addition to hashcode, sockets but also from NIO, array, string, Java 8 in addition to much more.
It has questions for both entry-level Java programmers in addition to senior developers alongside years of experience. No affair whether yous are a Java developer of 1, 2, 3, 4, 5, 6, 8, nine or fifty-fifty 10 years of experience, yous volition uncovering something interesting inwards this list. It contains questions which are super piece of cake to answer, in addition to also, a query which is tricky plenty for fifty-fifty seasoned Java programmers. If yous demand to a greater extent than questions in addition to so yous tin also cheque out this Java Interview Guide: 200+ Interview Questions alongside Answers
Given the listing is long in addition to nosotros receive got questions from everywhere, it's imperative that answers must endure short, concise in addition to crisp, no fluffing at all. So apart from this paragraph, yous volition solely listen from me is the questions in addition to answers, no to a greater extent than context, no to a greater extent than feedback in addition to no to a greater extent than evaluation.
For that, I receive got already written spider web log posts, where yous tin uncovering my views on a particular question, e.g. why I similar that question, what makes them challenging in addition to what form of reply yous should hold back from candidates.
This listing is a piffling flake unlike in addition to I encourage yous to portion questions in addition to answers inwards a similar way so that it should endure piece of cake to revise. I promise this listing tin endure a slap-up usage for both interviewer in addition to candidates, the interviewer can, of course, position a piffling diverseness on questions to convey novelty in addition to surprise element, which is of import for a goodness interview. While a candidate, tin expand in addition to testify their noesis nigh key areas of Java programming linguistic communication in addition to platform.
In 2018 in addition to inwards coming years the focus volition endure to a greater extent than on advanced concurrency concept, JVM internals, 32-bit vs 64-bit JVM, unit of measurement testing, in addition to create clean code. I am sure, i time yous read through this MEGA listing of Java interview question, yous should endure able to do good on both telephonic in addition to human face upward to human face upward programming interviews.
Java NIO in addition to JVM internals questions are best examples of that. You tin hold blueprint patterns also on the same listing but growing number of an experienced programmer are at nowadays good aware of GOF blueprint patterns in addition to when to usage them. I receive got also worked hard to hold this listing up-to-date to include what interviewers are asking inwards 2018 in addition to what volition endure their centre focus on coming years. To give yous an idea, this listing of Java interview questions includes next topics:
You guys are also lucky that nowadays in that location are some goodness books available to ready for Java interviews, i of them which I especially uncovering useful in addition to interesting to read is Java Programming Interview Exposed past times Markham. It volition take yous to some of the most of import topics for Java in addition to JEE interviews, worth reading fifty-fifty if yous are non preparing for Java interview.
1) Can nosotros brand array volatile inwards Java?
This is i of the tricky Java multi-threading questions yous volition run across inwards senior Java developer Interview. Yes, yous tin brand an array volatile inwards Java but solely the reference which is pointing to an array, non the whole array. What I mean, if i thread changes the reference variable to points to some other array, that volition render a volatile guarantee, but if multiple threads are changing private array elements they won't endure having happens earlier guarantee provided past times the volatile modifier.
2) Can volatile brand a non-atomic performance to atomic?
This some other goodness query I honey to inquire on volatile, mostly every bit a follow-up of the previous question. This query is also non piece of cake to reply because volatile is non nigh atomicity, but in that location are cases where yous tin usage a volatile variable to brand the performance atomic.
One illustration I receive got seen is having a long patch inwards your class. If yous know that a long patch is accessed past times to a greater extent than than i thread e.g. a counter, a cost patch or anything, yous ameliorate travel past times away far volatile. Why? because reading to a long variable is non atomic inwards Java in addition to done inwards ii steps, If i thread is writing or updating long value, it's possible for some other thread to run across one-half value (fist 32-bit). While reading/writing a volatile long or double (64 bit) is atomic.
3) What are practical uses of volatile modifier?
One of the practical usage of the volatile variable is to brand reading double in addition to long atomic. Both double in addition to long are 64-bit broad in addition to they are read inwards ii parts, commencement 32-bit commencement fourth dimension in addition to adjacent 32-bit 2nd time, which is non-atomic but volatile double in addition to long read is atomic inwards Java. Another usage of the volatile variable is to render a retentiveness barrier, only similar it is used inwards Disrupter framework. Basically, Java Memory model inserts a write barrier after yous write to a volatile variable in addition to a read barrier earlier yous read it. Which means, if yous write to volatile patch in addition to so it's guaranteed that whatever thread accessing that variable volition run across the value yous wrote in addition to anything yous did earlier doing that right into the thread is guaranteed to receive got happened in addition to whatever updated information values volition also endure visible to all threads, because the retentiveness barrier flushed all other writes to the cache.
4) What guarantee volatile variable provides? (answer)
volatile variables render the guarantee nigh ordering in addition to visibility e.g. volatile assignment cannot endure re-ordered alongside other statements but inwards the absence of whatever synchronization didactics compiler, JVM or JIT are gratuitous to reorder statements for ameliorate performance. volatile also provides the happens-before guarantee which ensures changes made inwards i thread is visible to others. In some cases volatile also render atomicity e.g. reading 64-bit information types similar long in addition to double are non atomic but read of volatile double or long is atomic.
5) Which i would endure piece of cake to write? synchronization code for 10 threads or 2 threads?
In damage of writing code, both volition endure of same complexity because synchronization code is independent of a number of threads. Choice of synchronization though depends upon a number of threads because the number of thread nowadays to a greater extent than contention, so yous travel past times away for advanced synchronization technique e.g. lock stripping, which requires to a greater extent than complex code in addition to expertise.
6) How do yous telephone phone wait() method? using if block or loop? Why? (answer)
wait() method should ever endure called inwards loop because it's possible that until thread gets CPU to start running i time again the status mightiness non hold, so it's ever ameliorate to cheque status inwards loop earlier proceeding. Here is the criterion idiom of using hold back in addition to notify method inwards Java:
7) What is imitation sharing inwards the context of multi-threading?
imitation sharing is i of the well-known performance issues on multi-core systems, where each procedure has its local cache. imitation sharing occurs when threads on unlike processor modify variables that reside on same cache delineate every bit shown inwards the next image:
False sharing is real hard to uncovering because the thread may endure accessing completely unlike global variables that tumble out to endure relatively closed together inwards memory. Like many concurrency issues, the primary way to avoid imitation sharing is careful code review in addition to aligning your information construction alongside the size of a cache line.
8) What is busy spin? Why should yous usage it?
Busy spin is i of the technique to hold back for events without releasing CPU. It's often done to avoid losing information inwards CPU cached which is lost if the thread is paused in addition to resumed inwards some other core. So, if yous are working on depression latency arrangement where your guild processing thread currently doesn't receive got whatever order, instead of sleeping or calling wait(), yous tin only loop in addition to and so i time again cheque the queue for novel messages. It's solely beneficial if yous demand to hold back for a real small-scale amount of fourth dimension e.g. inwards micro seconds or nano seconds. LMAX Disrupter framework, a high-performance inter-thread messaging library has a BusySpinWaitStrategy which is based on this concept in addition to uses a busy spin loop for EventProcessors waiting on the barrier.
9) How do yous take thread dump inwards Java?
You tin take a thread dump of Java application inwards Linux past times using kill -3 PID, where PID is the procedure id of Java process. In Windows, yous tin press Ctrl + Break. This volition instruct JVM to impress thread dump inwards criterion out or err in addition to it could travel past times away to console or log file depending upon your application configuration. If yous receive got used Tomcat in addition to so when
10) is Swing thread-safe? (answer)
No, Swing is non thread-safe. You cannot update Swing components e.g. JTable, JList or JPanel from whatever thread, inwards fact, they must endure updated from GUI or AWT thread. That's why swings render invokeAndWait() in addition to invokeLater() method to asking GUI update from whatever other threads. This methods position update asking inwards AWT threads queue in addition to tin hold back till update or render straightaway for an asynchronous update. You tin also cheque the detailed reply to larn more.
11) What is a thread local variable inwards Java? (answer)
Thread-local variables are variables confined to a thread, its similar thread's ain re-create which is non shared betwixt multiple threads. Java provides a ThreadLocal shape to back upward thread-local variables. It's i of the many ways to attain thread-safety. Though endure careful spell using thread local variable inwards manged surround e.g. alongside spider web servers where worker thread out lives whatever application variable. Any thread local variable which is non removed i time its piece of work is done tin potentially drive a retentiveness leak inwards Java application.
12) Write wait-notify code for producer-consumer problem? (answer)
Please run across the reply for a code example. Just recall to telephone phone wait() in addition to notify() method from synchronized block in addition to testify waiting for status on the loop instead of if block.
13) Write code for thread-safe Singleton inwards Java? (answer)
Please run across the reply for a code illustration in addition to stair past times stair guide to creating thread-safe singleton shape inwards Java. When nosotros say thread-safe, which agency Singleton should stay singleton fifty-fifty if initialization occurs inwards the illustration of multiple threads. Using Java enum every bit Singleton shape is i of the easiest ways to create a thread-safe singleton inwards Java.
14) The divergence betwixt slumber in addition to hold back inwards Java? (answer)
Though both are used to suspension currently running thread, sleep() is genuinely meant for brusk suspension because it doesn't release lock, spell wait() is meant for conditional hold back in addition to that's why it release lock which tin in addition to so endure acquired past times some other thread to alter the status on which it is waiting.
15) What is an immutable object? How do yous create an Immutable object inwards Java? (answer)
Immutable objects are those whose state cannot endure changed i time created. Any modification volition number inwards a novel object e.g. String, Integer, and other wrapper class. Please run across the reply for stair past times stair guide to creating Immutable shape inwards Java.
16) Can nosotros create an Immutable object, which contains a mutable object?
Yes, its possible to create an Immutable object which may incorporate a mutable object, yous only demand to endure a piffling flake careful non to portion the reference of the mutable component, instead, yous should render a re-create of it if yous receive got to. Most mutual illustration is an Object which incorporate the reference of java.util.Date object.
17) What is the right information type to correspond a cost inwards Java? (answer)
BigDecimal if retentiveness is non a delineate of piece of work concern in addition to Performance is non critical, otherwise double alongside predefined precision.
18) How do yous convert bytes to String? (answer)
yous tin convert bytes to the string using string constructor which accepts byte[], only brand certainly that right grapheme encoding otherwise platform's default grapheme encoding volition endure used which may or may non endure same.
19) How do yous convert bytes to long inwards Java? (answer)
This questions if for yous to reply :-)
20) Can nosotros cast an int value into byte variable? what volition tumble out if the value of int is larger than byte?
Yes, nosotros tin cast but int is 32 flake long inwards coffee spell byte is 8 flake long inwards coffee so when yous cast an int to byte higher 24 bits are lost in addition to a byte tin solely concur a value from -128 to 128.
21) There are ii classes B extends H5N1 in addition to C extends B, Can nosotros cast B into C e.g. C = (C) B; (answer)
22) Which shape contains clone method? Cloneable or Object? (answer)
java.lang.Cloneable is marking interface in addition to doesn't incorporate whatever method clone method is defined inwards the object class. It is also knowing that clone() is a native method agency it's implemented inwards C or C++ or whatever other native language.
23) Is ++ operator is thread-safe inwards Java? (answer)
No it's non a thread condom operator because its involve multiple instructions similar reading a value, incriminating it in addition to storing it dorsum into retentiveness which tin endure overlapped betwixt multiple threads.
24) Difference betwixt a = a + b in addition to a += b ? (answer)
The += operator implicitly cast the number of add-on into the type of variable used to concur the result. When yous add together ii integral variable e.g. variable of type byte, short, or int in addition to so they are commencement promoted to int in addition to them add-on happens. If number of add-on is to a greater extent than than maximum value of a in addition to so a + b volition give compile fourth dimension fault but a += b volition endure ok every bit shown below
25) Can I shop a double value inwards a long variable without casting? (answer)
No, yous cannot shop a double value into a long variable without casting because the attain of double is to a greater extent than that long in addition to yous nosotros demand to type cast. It's non dificult to reply this query but many develoepr acquire it wrong due to confusion on which i is bigger betwixt double in addition to long inwards Java.
26) What volition this render 3*0.1 == 0.3? truthful or false? (answer)
This is i of the genuinely tricky questions. Out of 100, solely five developers answered this query in addition to solely of them receive got explained the concept correctly. The brusk reply is imitation because some floating dot numbers tin non endure represented exactly.
27) Which i volition take to a greater extent than memory, an int or Integer? (answer)
An Integer object volition take to a greater extent than retentiveness an Integer is the an object in addition to it store meta information overhead nigh the object in addition to int is primitive type so its takes less space.
28) Why is String Immutable inwards Java? (answer)
One of my favorite Java interview question. The String is Immutable inwards coffee because coffee designer thought that string volition endure heavily used in addition to making it immutable allow some optimization piece of cake sharing same String object betwixt multiple clients. See the link for the to a greater extent than detailed answer. This is a slap-up query for Java programmers alongside less experience every bit it gives them nutrient for thought, to think nigh how things industrial plant inwards Java, what Jave designers mightiness receive got thought when they created String shape etc.
29) Can nosotros usage String inwards the switch case? (answer)
Yes from Java vii onward nosotros tin usage String inwards switch illustration but it is only syntactic sugar. Internally string hash code is used for the switch. See the detaiedl reply for to a greater extent than explanation in addition to discussion.
30) What is constructor chaining inwards Java? (answer)
When yous telephone phone i constructor from other than it's known every bit constructor chaining inwards Java. This happens when yous receive got multiple, overloaded constructor inwards the class.
31) What is the size of int inwards 64-bit JVM?
The size of an int variable is constant inwards Java, it's ever 32-bit irrespective of platform. Which agency the size of primitive int is same inwards both 32-bit in addition to 64-bit Java virtual machine.
32) The divergence betwixt Serial in addition to Parallel Garbage Collector? (answer)
Even though both the series in addition to parallel collectors drive a stop-the-world suspension during Garbage collection. The chief divergence betwixt them is that a series collector is a default copying collector which uses solely i GC thread for garbage collection spell a parallel collector uses multiple GC threads for garbage collection.
33) What is the size of an int variable inwards 32-bit in addition to 64-bit JVM? (answer)
The size of int is same inwards both 32-bit in addition to 64-bit JVM, it's ever 32 bits or 4 bytes.
34) H5N1 divergence betwixt WeakReference in addition to SoftReference inwards Java? (answer)
Though both WeakReference in addition to SoftReference helps garbage collector in addition to retentiveness efficient, WeakReference becomes eligible for garbage collection every bit presently every bit in conclusion strong reference is lost but SoftReference fifty-fifty thought it tin non foreclose GC, it tin delay it until JVM absolutely demand memory.
35) How do WeakHashMap works? (answer)
WeakHashMap industrial plant similar a normal HashMap but uses WeakReference for keys, which agency if the key object doesn't receive got whatever reference in addition to so both key/value mapping volition acquire eligible for garbage collection.
36) What is -XX:+UseCompressedOops JVM option? Why usage it? (answer)
When yous travel past times away migrate your Java application from 32-bit to 64-bit JVM, the heap requirement all of a abrupt increases, almost double, due to increasing size of ordinary object pointer from 32 flake to 64 bit. This also adversely deport on how much information yous tin hold inwards CPU cache, which is much smaller than memory. Since chief motivation for moving to 64-bit JVM is to specify large heap size, yous tin salve some retentiveness past times using compressed OOP. By using -XX:+UseCompressedOops, JVM uses 32-bit OOP instead of 64-bit OOP.
37) How do yous uncovering if JVM is 32-bit or 64-bit from Java Program? (answer)
You tin uncovering that past times checking some arrangement properties like sun.arch.data.model or os.arch
38) What is the maximum heap size of 32-bit in addition to 64-bit JVM? (answer)
Theoretically, the maximum heap retentiveness yous tin assign to a 32-bit JVM is 2^32 which is 4GB but practically the bound is much smaller. It also varies betwixt operating systems e.g. shape 1.5GB inwards Windows to almost 3GB inwards Solaris. 64-bit JVM allows yous to specify larger heap size, theoretically 2^64 which is quite large but practically yous tin specify heap infinite upward to 100GBs. There are fifty-fifty JVM e.g. Azul where heap infinite of M gigs is also possible.
39) What is the divergence betwixt JRE, JDK, JVM in addition to JIT? (answer)
JRE stands for Java run-time in addition to it's required to run Java application. JDK stands for Java evolution kit in addition to provides tools to prepare Java computer program e.g. Java compiler. It also contains JRE. The JVM stands for Java virtual machine in addition to it's the procedure responsible for running Java application. The JIT stands for Just In Time compilation in addition to helps to boost the performance of Java application past times converting Java byte code into native code when the crossed certainly threshold i.e. mainly hot code is converted into native code.
40) Explain Java Heap infinite in addition to Garbage collection? (answer)
When a Java procedure is started using coffee command, retentiveness is allocated to it. Part of this retentiveness is used to create heap space, which is used to allocate retentiveness to objects whenever they are created inwards the program. Garbage collection is the procedure within JVM which reclaims retentiveness from dead objects for futurity allocation.
41) Can yous guarantee the garbage collection process? (answer)
No, yous cannot guarantee the garbage collection, though yous tin brand a asking using System.gc() or Runtime.gc() method.
42) How do yous uncovering retentiveness usage from Java program? How much pct of the heap is used?
You tin usage retentiveness related methods from java.lang.Runtime shape to acquire the gratuitous memory, total retentiveness in addition to maximum heap retentiveness inwards Java. By using these methods, yous tin uncovering out how many percents of the heap is used in addition to how much heap infinite is remaining. Runtime.freeMemory() render amount of gratuitous retentiveness inwards bytes, Runtime.totalMemory() returns total retentiveness inwards bytes in addition to Runtime.maxMemory() returns maximum retentiveness inwards bytes.
43) What is the divergence betwixt stack in addition to heap inwards Java? (answer)
Stack in addition to heap are unlike retentiveness areas inwards the JVM in addition to they are used for unlike purposes. The stack is used to concur method frames in addition to local variables spell objects are ever allocated retentiveness from the heap. The stack is ordinarily much smaller than heap retentiveness in addition to also didn't shared betwixt multiple threads, but heap is shared amid all threads inwards JVM.
The a = b does object reference matching if both a in addition to b are an object in addition to solely render truthful if both are pointing to the same object inwards the heap space, on the other hand, a.equals(b) is used for logical mapping in addition to its expected from an object to override this method to render logical equality. For example, String shape overrides this equals() method so that yous tin compare ii Strings, which are the unlike object but contains same letters.
45) What is a.hashCode() used for? How is it related to a.equals(b)? (answer)
hashCode() method returns an int hash value corresponding to an object. It's used inwards hash based collection classes e.g Hashtable, HashMap, LinkedHashMap in addition to so on. It's real tightly related to equals() method. According to Java specification, ii objects which are equal to each other using equals() method must receive got same hash code.
46) Difference betwixt final, finalize in addition to finally? (answer)
The concluding is a modifier which yous tin apply to variable, methods in addition to classes. If yous brand a variable concluding it agency its value cannot endure changed i time initialized. finalize is a method, which is called only earlier an object is a garbage collected, giving it in conclusion adventure to resurrect itself, but the telephone phone to finalize is non guaranteed. finally is a keyword which is used inwards exception treatment along alongside attempt in addition to catch. the finally block is ever executed irrespective of whether an exception is thrown from attempt block or not.
47) What is a compile fourth dimension constant inwards Java? What is the endangerment of using it?
world static concluding variables are also known every bit a compile fourth dimension constant, earth is optional there. They are replaced alongside actual values at compile fourth dimension because compiler know their value up-front in addition to also knows that it cannot endure changed during run-time. One of the occupation alongside this is that if yous happened to usage a world static concluding variable from some in-house or 3rd political party library in addition to their value changed after than your customer volition nevertheless endure using erstwhile value fifty-fifty after yous deploy a novel version of JARs. To avoid that, brand certainly yous compile your computer program when yous upgrade dependency JAR files.
48) The divergence betwixt List, Set, Map, in addition to Queue inwards Java? (answer)
The listing is an ordered collection which allows duplicate. It also has an implementation which provides constant fourth dimension index based access, but that is non guaranteed past times List interface. Set is unordered collection which
49) Difference betwixt poll() in addition to remove() method?
Both poll() in addition to remove() take out the object from the Queue but if poll() fails in addition to so it returns zero but if take away fails it throws Exception.
50) The divergence betwixt LinkedHashMap in addition to PriorityQueue inwards Java? (answer)
PriorityQueue guarantees that lowest or highest priority chemical element ever stay at the caput of the queue, but LinkedHashMap maintains the guild on which elements are inserted. When yous iterate over a PriorityQueue, iterator doesn't guarantee whatever guild but iterator of LinkedHashMap does guarantee the guild on which elements are inserted.
51) Difference betwixt ArrayList in addition to LinkedList inwards Java? (answer)
The obvious divergence betwixt them is that ArrrayList is backed past times array information structure, supprots random access in addition to LinkedList is backed past times linked listing information construction in addition to doesn't supprot random access. Accessing an chemical element alongside the index is O(1) inwards ArrayList but its O(n) inwards LinkedList. See the reply for to a greater extent than detailed discussion.
52) What is a duad of ways that yous could sort a collection? (answer)
You tin either usage the Sorted collection similar TreeSet or TreeMap or yous tin sort using the ordered collection similar a listing in addition to using Collections.sort() method.
53) How do yous impress Array inwards Java? (answer)
You tin impress an array past times using the Arrays.toString() in addition to Arrays.deepToString() method. Since array doesn't implement toString() past times itself, only passing an array to System.out.println() volition non impress its contents but Arrays.toString() volition impress each element.
There are many differences betwixt these ii classes, some of them are following:
a) Hashtable is a legacy shape in addition to nowadays from JDK 1, HashMap was added later.
b) Hashtable is synchronized in addition to slower but HashMap is non synchronized in addition to faster.
c) Hashtable doesn't allow zero keys but HashMap allows i zero key.
See the reply for to a greater extent than differences betwixt HashMap in addition to Hashtable inwards Java.
57) How HashSet industrial plant internally inwards Java? (answer)
HashSet is internally implemented using an HashMap. Since a Map needs key in addition to value, a default value is used for all keys. Similar to HashMap, HashSet doesn't allow duplicate keys in addition to solely i zero key, I hateful yous tin solely shop i zero object inwards HashSet.
58) Write code to take away elements from ArrayList spell iterating? (answer)
Key hither is to cheque whether candidate uses ArrayList's remove() or Iterator's remove(). Here is the sample code which uses right way o take away elements from ArrayList spell looping over in addition to avoids ConcurrentModificationException.
59) Can I write my ain container shape in addition to usage it inwards the for-each loop?
Yes, yous tin write your ain container class. You demand to implement the Iterable interface if yous desire to loop over advanced for loop inwards Java, though. If yous implement Collection in addition to so yous past times default acquire that property.
60) What is default size of ArrayList in addition to HashMap inwards Java? (answer)
As of Java vii now, default size of ArrayList is 10 in addition to default capacity of HashMap is 16, it must endure powerfulness of 2. Here is code snippet from ArrayList and HashMap shape :
61) Is it possible for ii unequal objects to receive got the same hashcode?
Yes, ii unequal objects tin receive got same hashcode that's why collision tumble out inwards a hashmap.
the equal hashcode contract solely says that ii equal objects must receive got the same hashcode it doesn't say anything nigh the unequal object.
62) Can ii equal object receive got the unlike hash code?
No, thats non possible according to hash code contract.
63) Can nosotros usage random numbers inwards the hashcode() method? (answer)
No, because hashcode of an object should endure ever same. See the reply to learning to a greater extent than nigh things to recall spell overriding hashCode() method inwards Java.
64) What is the divergence betwixt Comparator in addition to Comparable inwards Java? (answer)
The Comparable interface is used to define the natural guild of object spell Comparator is used to define custom order. Comparable tin endure ever one, but nosotros tin receive got multiple comparators to define customized guild for objects.
65) Why yous demand to override hashcode, when yous override equals inwards Java? (answer)
Because equals receive got code contract mandates to override equals in addition to hashcode together .since many container shape similar HashMap or HashSet depends on hashcode in addition to equals contract.
66) In my Java program, I receive got 3 sockets? How many threads I volition demand to grip that?
67) How do yous create ByteBuffer inwards Java?
68) How do yous write in addition to read from ByteBuffer inwards Java?
69) Is Java BIG endian or LITTLE endian?
70) What is the byte guild of ByteBuffer?
71) The divergence betwixt direct buffer in addition to non-direct buffer inwards Java? (answer)
72) What is the retentiveness mapped buffer inwards Java? (answer)
73) What is TCP NO DELAY socket option?
74) What is the divergence betwixt TCP in addition to UDP protocol? (answer)
75) The divergence betwixt ByteBuffer in addition to StringBuffer inwards Java? (answer)
76) What best practices yous follow spell writing multi-threaded code inwards Java? (answer)
Here are duad of best practices which I follow spell writing concurrent code inwards Java:
a) Always squall your thread, this volition aid inwards debugging.
b) minimize the orbit of synchronization, instead of making whole method synchronized, solely critical department should endure synchronized.
c) prefer volatile over synchronized if yous tin can.
e) usage higher aeroplane concurrency utilities instead of waitn() in addition to notify for inter thread communication e.g. BlockingQueue, CountDownLatch in addition to Semeaphore.
e) Prefer concurrent collection over synchronized collection inwards Java. They render ameliorate scalability.
77) Tell me few best practices yous apply spell using Collections inwards Java? (answer)
Here are duad of best practices I follow spell using Collectionc classes from Java:
a) Always usage the right collection e.g. if yous demand non-synchronized listing in addition to so usage ArrayList in addition to non Vector.
b) Prefer concurrent collection over synchronized collection because they are to a greater extent than scalable.
c) Always usage interface to a correspond in addition to access a collection e.g. usage List to shop ArrayList, Map to shop HashMap in addition to so on.
d) Use iterator to loop over collection.
e) Always usage generics alongside collection.
78) Can yous tell us at to the lowest degree five best practise yous usage spell using threads inwards Java? (answer)
This is similar to the previous query in addition to yous tin usage the reply given there. Particularly alongside thread, yous should:
a) squall your thread
b) hold your task in addition to thread separate, usage Runnable or Callable alongside thread puddle executor.
c) usage thread pool
d) usage volatile to betoken compiler nigh ordering, visibility, in addition to atomicity.
e) avoid thread local variable because wrong usage of ThreadLocal shape inwards Java tin create a retentiveness leak.
Look in that location are many best practices in addition to I give extra points to the developer which convey something new, something fifty-fifty I don't know. I brand certainly to inquire this query to Java developers of 8 to 10 years of experience only to justice his hands on experience in addition to knowledge.
79) Name five IO best practices? (answer)
IO is real of import for performance of your Java application. Ideally yous should avoid IO inwards critical path of your application. Here are duad of Java IO best practices yous tin follow:
80) Name five JDBC best practices your follow? (answer)
Another goodness Java best practices for experienced Java developer of vii to 8 years experience. Why it's important? because they are the ones which laid the tendency inwards the code in addition to educate junior developers. There are many best practices in addition to yous tin squall every bit per your confort in addition to conviniece. Here are some of the to a greater extent than mutual ones:
a) usage batch declaration for inserting in addition to updating data.
b) usage PreparedStatement to avoid SQL exception in addition to ameliorate performance.
c) usage database connectedness pool
d) access resultset using column squall instead of column indexes.
e) Don't generate dynamic SQL past times concatenating String alongside user input.
81) Name duad of method overloading best practices inwards Java? (answer)
Here are some best practices yous tin follow spell overloading a method inwards Java to avoid confusion alongside auto-boxing:
a) Don't overload method where i accepts int in addition to other accepts Integer.
b) Don't overload method where number of declaration is same in addition to solely guild of declaration is different.
c) Use varargs after overloaded methods has to a greater extent than than five arguments.
82) Does SimpleDateFormat is condom to usage inwards the multi-threaded program? (answer)
No, unfortunately, DateFormat in addition to all its implementations including SimpleDateFormat is non thread-safe, so should non endure used inwards the multi-threaded computer program until external thread-safety measures are applied e.g. confining SimpleDateFormat object into a ThreadLocal variable. If yous don't do that, yous volition acquire an wrong number spell parsing or formatting dates inwards Java. Though, for all practical appointment fourth dimension purpose, I highly recommend joda-time library.
83) How do yous format a appointment inwards Java? e.g. inwards the ddMMyyyy format? (answer)
You tin either usage SimpleDateFormat shape or joda-time library to format appointment inwards Java. DateFormat shape allows yous to format appointment on many pop formats. Please run across the reply for code samples to format appointment into unlike formats e.g. dd-MM-yyyy or ddMMyyyy.
84) How do yous demo timezone inwards formatted appointment inwards Java? (answer)
85) The divergence betwixt java.util.Date in addition to java.sql.Date inwards Java? (answer)
86) How to yous calculate the divergence betwixt ii dates inwards Java? (program)
87) How do yous convert a String(YYYYMMDD) to appointment inwards Java? (answer)
You tin usage PowerMock library to testify static methods inwards Java.
90) How to do yous testify a method for an exception using JUnit? (answer)
91) Which unit of measurement testing libraries yous receive got used for testing Java programs? (answer)
92) What is the divergence betwixt @Before in addition to @BeforeClass annotation? (answer)
94) How to write LRU cache inwards Java using Generics? (answer)
95) Write a Java computer program to convert bytes to long? (answer)
96) How to contrary a String inwards Java without using StringBuffer? (solution)
98) How do yous cheque if ii given String are anagrams? (solution)
99) How to impress all permutation of a String inwards Java? (solution)
100) How do yous impress duplicate elements from an array inwards Java? (solution)
101) How to convert String to int inwards Java? (solution)
102) How to swap ii integers without using temp variable? (solution)
103) What is the interface? Why yous usage it if yous cannot write anything concrete on it?
The interface is used to define API. It tells nigh the contract your classes volition follow. It also supports abstraction because a customer tin usage interface method to leverage multiple implementations e.g. past times using List interface yous tin take wages of random access of ArrayList every bit good every bit flexible insertion in addition to deletion of LinkedList. The interface doesn't allow yous to write code to hold things abstract but from Java 8 yous tin declare static in addition to default methods within interface which are concrete.
104) The divergence betwixt abstract shape in addition to interface inwards Java? (answer)
There are multiple differences betwixt abstract shape in addition to interface inwards Java, but the most of import i is Java's restriction on allowing a shape to extend only i shape but allows it to implement multiple interfaces. An abstract shape is goodness to define default conduct for a solid unit of measurement of class, but the interface is goodness to define Type which is after used to leverage Polymorphism. Please cheque the reply for a to a greater extent than thorough give-and-take of this question.
105) Which blueprint pattern receive got yous used inwards your production code? apart from Singleton?
This is something yous tin reply from your experience. You tin to a greater extent than often than non say nigh dependency injection, mill pattern, decorator pattern or observer pattern, whichever yous receive got used. Though endure prepared to reply follow-up query based upon the pattern yous choose.
106) Can yous explicate Liskov Substitution principle? (answer)
This is i of the toughest questions I receive got asked inwards Java interviews. Out of 50 candidates, I receive got almost asked solely five receive got managed to reply it. I am non posting an reply to this query every bit I similar yous to do some research, practise in addition to pass some fourth dimension to sympathize this confusing regulation well.
107) What is Law of Demeter violation? Why it matters? (answer)
Believe it or not, Java is all nigh application programming in addition to structuring code. If you receive got goodness noesis of common coding best practices, patterns in addition to what non to do than solely yous tin write character code. Law of Demeter suggests yous "talk to friends in addition to non stranger", so used to cut down coupling betwixt classes.
108) What is Adapter pattern? When to usage it?
Another oftentimes asked Java blueprint pattern questions. It provides interface conversion. If your customer is using some interface but yous receive got something else, yous tin write an Adapter to span them together. This is goodness for Java software engineer having 2 to 3 years experience because the query is neither hard nor tricky but requires noesis of OOP blueprint patterns.
109) What is "dependency injection" in addition to "inversion of control"? Why would someone usage it? (answer)
110) What is an abstract class? How is it unlike from an interface? Why would yous usage it? (answer)
One to a greater extent than classic query from Programming Job interviews, it is every bit erstwhile every bit chuck Norris. An abstract shape is a shape which tin receive got state, code in addition to implementation, but an interface is a contract which is totally abstract. Since I receive got answered it many times, I am solely giving yous the gist hither but yous should read the article linked to reply to larn this useful concept inwards much to a greater extent than detail.
111) Which i is ameliorate constructor injection or setter dependency injection? (answer)
Each has their ain wages in addition to disadvantage. Constructor injection guaranteed that shape volition endure initialized alongside all its dependency, but setter injection provides flexibility to laid an optional dependency. Setter injection is also to a greater extent than readable if yous are using an XML file to pull dependency. Rule of pollex is to usage constructor injection for mandatory dependency in addition to usage setter injection for optional dependency.
112) What is divergence betwixt dependency injection in addition to mill blueprint pattern? (answer)
Though both patterns aid to take out object creation component division from application logic, usage of dependency injection results inwards cleaner code than mill pattern. By using dependency injection, your classes are cipher but POJO which solely knows nigh dependency but doesn't tending how they are acquired. In the illustration of mill pattern, the shape also needs to know nigh mill to acquire dependency. hence, DI results inwards to a greater extent than testable classes than mill pattern. Please run across the reply for a to a greater extent than detailed give-and-take on this topic.
113) Difference betwixt Adapter in addition to Decorator pattern? (answer)
Though the construction of Adapter in addition to Decorator pattern is similar, the divergence comes on the intent of each pattern. The adapter pattern is used to span the gap betwixt ii interfaces, but Decorator pattern is used to add together novel functionality into the shape without the modifying existing code.
114) Difference betwixt Adapter in addition to Proxy Pattern? (answer)
Similar to the previous question, the divergence betwixt Adapter in addition to Proxy patterns is inwards their intent. Since both Adapter in addition to Proxy pattern encapsulate the shape which genuinely does the job, so number inwards the same structure, but Adapter pattern is used for interface conversion spell the Proxy pattern is used to add together an extra aeroplane of indirection to back upward distribute, controlled or intelligent access.
115) What is Template method pattern? (answer)
Template pattern provides an outline of an algorithm in addition to lets yous configure or customize its steps. For examples, yous tin persuasion a sorting algorithm every bit a template to sort object. It defines steps for sorting but permit yous configure how to compare them using Comparable or something similar inwards some other language. The method which outlines the algorithms is also known every bit template method.
116) When do yous usage Visitor blueprint pattern? (answer)
The visitor pattern is a solution of occupation where yous demand to add together performance on a shape hierarchy but without touching them. This pattern uses double dispatch to add together some other aeroplane of indirection.
117) When do yous usage Composite blueprint pattern? (answer)
Composite blueprint pattern arranges objects into tree structures to correspond part-whole hierarchies. It allows clients care for private objects in addition to container of objects uniformly. Use Composite pattern when yous desire to correspond part-whole hierarchies of objects.
118) The divergence betwixt Inheritance in addition to Composition? (answer)
Though both allows code reuse, Composition is to a greater extent than flexible than Inheritance because it allows yous to switch to some other implementation at run-time. Code written using Composition is also easier to testify than code involving inheritance hierarchies.
119) Describe overloading in addition to overriding inwards Java? (answer)
Both overloading in addition to overriding allow yous to write ii methods of unlike functionality but alongside the same name, but overloading is compile fourth dimension activity spell overriding is run-time activity. Though yous tin overload a method inwards the same class, but yous tin solely override a method inwards tyke classes. Inheritance is necessary for overriding.
120) The divergence betwixt nested world static shape in addition to a top aeroplane shape inwards Java? (answer)
You tin receive got to a greater extent than than i nested world static shape within i class, but yous tin solely receive got i top-level world shape inwards a Java rootage file in addition to its squall must endure same every bit the squall of Java rootage file.
121) Difference betwixt Composition, Aggregation in addition to Association inwards OOP? (answer)
If ii objects are related to each other, they are said to endure associated alongside each other. Composition in addition to Aggregation are ii forms of association inwards object-oriented programming. The composition is stronger association than Aggregation. In Composition, i object is OWNER of some other object spell inwards Aggregation i object is only USER of some other object. If an object H5N1 is composed of object B in addition to so B doesn't be if H5N1 ceased to exists, but if object H5N1 is only an aggregation of object B in addition to so B tin exists fifty-fifty if H5N1 ceased to exist.
122) Give me an illustration of blueprint pattern which is based upon opened upward closed principle? (answer)
This is i of the practical questions I inquire experienced Java programmer. I hold back them to know nigh OOP blueprint principles every bit good every bit patterns. Open closed blueprint regulation asserts that your code should endure opened upward for extension but closed for modification. Which agency if yous desire to add together novel functionality, yous tin add together it easily using the novel code but without touching already tried in addition to tested code. There are several blueprint patterns which are based upon opened upward closed blueprint regulation e.g. Strategy pattern if yous demand a novel strategy, only implement the interface in addition to configure, no demand to modify centre logic. One working illustration is Collections.sort() method which is based on Strategy pattern in addition to follows the open-closed principle, yous don't modify sort() method to sort a novel object, what yous do is only implement Comparator inwards your ain way.
123) Difference betwixt Abstract mill in addition to Prototype blueprint pattern? (answer)
This is the practise query for you, If yous are feeling bored only reading in addition to itching to write something, why non write the reply to this question. I would honey to run across an illustration the, which should reply where yous should usage the Abstract mill pattern in addition to where is the Prototype pattern is to a greater extent than suitable.
124) When do yous usage Flyweight pattern? (answer)
This is some other pop query from the blueprint pattern. Many Java developers alongside 4 to half-dozen years of experience know the Definition but failed to give whatever concrete example. Since many of yous mightiness non receive got used this pattern, it's ameliorate to appear examples from JDK. You are to a greater extent than probable receive got used them earlier in addition to they are piece of cake to recall every bit well. Now let's run across the answer.
Flyweight pattern allows yous to portion object to back upward large numbers without genuinely creating likewise many objects. In guild to use Flyweight pattern, yous demand to brand your object Immutable so that they tin endure safely shared. String puddle in addition to puddle of Integer in addition to Long object inwards JDK are goodness examples of Flyweight pattern.
125) The divergence betwixt nested static shape in addition to top aeroplane class? (answer)
One of the telephone substitution questions from Java basics. I inquire this query solely to junior Java developers of 1 to 2 years of experience every bit it's likewise piece of cake for an experience Java programmers. The reply is simple, a world top aeroplane shape must receive got the same squall every bit the squall of the rootage file, in that location is no such requirement for nested static class. H5N1 nested shape is ever within a top aeroplane shape in addition to yous demand to usage the squall of the top-level shape to refer nested static shape e.g. HashMap.Entry is a nested static class, where HashMap is a top aeroplane shape in addition to Entry is nested static class.
126) Can yous write a regular facial expression to cheque if String is a number? (solution)
If yous are taking Java interviews in addition to so yous should inquire at to the lowest degree i query on the regular expression. This clearly differentiates an average programmer alongside a goodness programmer. Since i of the traits of a goodness developer is to know tools, regex is the best tool for searching something inwards the log file, preparing reports etc. Anyway, reply to this query is, a numeric String tin solely incorporate digits i.e. 0 to nine and + in addition to - sign that likewise at start of the String, past times using this information yous tin write next regular facial expression to cheque if given String is number or not
127) The divergence betwixt checked in addition to unchecked Exception inwards Java? (answer)
checked exception is checked past times the compiler at compile time. It's mandatory for a method to either grip the checked exception or declare them inwards their throws clause. These are the ones which are a sub shape of Exception but doesn't descend from RuntimeException. The unchecked exception is the descendant of RuntimeException in addition to non checked past times the compiler at compile time. This query is at nowadays becoming less pop in addition to yous would solely uncovering this alongside interviews alongside small-scale companies, both investment banks in addition to startups are moved on from this question.
128) The divergence betwixt throw in addition to throws inwards Java? (answer)
the throw is used to genuinely throw an instance of java.lang.Throwable class, which agency yous tin throw both Error in addition to Exception using throw keyword e.g.
On the other hand, throws is used every bit component division of method annunciation in addition to signals which form of exceptions are thrown past times this method so that its caller tin grip them. It's mandatory to declare whatever unhandled checked exception inwards throws clause inwards Java. Like the previous question, this is some other oftentimes asked Java interview query from errors in addition to exception theme but likewise piece of cake to answer.
129) The divergence betwixt Serializable in addition to Externalizable inwards Java? (answer)
This is i of the oftentimes asked questions from Java Serialization. The interviewer has been asking this query since the twenty-four threescore minutes menstruum Serialization was introduced inwards Java, but yet solely a few goodness candidate tin reply this query alongside some confidence in addition to practical knowledge. Serializable interface is used to brand Java classes serializable so that they tin endure transferred over network or their state tin endure saved on disk, but it leverages default serialization built-in JVM, which is expensive, delicate in addition to non secure. Externalizable allows yous to fully command the Serialization process, specify a custom binary format in addition to add together to a greater extent than security measure.
130) The divergence betwixt DOM in addition to SAX parser inwards Java? (answer)
Another mutual Java query but from XML parsing topic. It's rather uncomplicated to reply in addition to that's why many interviewers prefers to inquire this query on the telephonic round. DOM parser loads the whole XML into retentiveness to create a tree based DOM model which helps it apace locate nodes in addition to brand a alter inwards the construction of XML spell SAX parser is an trial based parser in addition to doesn't charge the whole XML into memory. Due to this argue DOM is faster than SAX but require to a greater extent than retentiveness in addition to non suitable to parse large XML files.
131) Tell me 3 features introduced on JDK 1.7? (answer)
This is i of the goodness questions I inquire to cheque whether the candidate is aware of recent evolution inwards Java technology scientific discipline infinite or not. Even though JDK vii was non a large bang release similar JDK five or JDK 8, it nevertheless has a lot of goodness characteristic to count on e.g. try-with-resource statements, which gratuitous yous from closing streams in addition to resources when yous are done alongside that, Java automatically closes that. Fork-Join puddle to implement something similar the Map-reduce pattern inwards Java. Allowing String variable in addition to literal into switch statements. Diamond operator for improved type inference, no demand to declare generic type on the right-hand side of variable annunciation anymore, results inwards to a greater extent than readable in addition to succinct code. Another worth noting characteristic introduced was improved exception treatment e.g. allowing yous to grab multiple exceptions inwards the same grab block.
132) Tell me five features introduced inwards JDK 1.8? (answer)
This is the follow-up query of the previous one. Java 8 is path breaking release inwards Java's history, hither are the top five features from JDK 8 release
133) What is the divergence betwixt Maven in addition to ANT inwards Java? (answer)
Another slap-up query to cheque the all circular noesis of Java developers. It's piece of cake to reply questions from centre Java but when yous inquire nigh setting things up, edifice Java artifacts, many Java software engineer struggles. Coming dorsum to the reply of this question, Though both are build tool in addition to used to create Java application build, Maven is much to a greater extent than than that. It provides criterion construction for Java projection based upon "convention over configuration" concept in addition to automatically care dependencies (JAR files on which your application is dependent) for Java application. Please run across the reply for to a greater extent than differences betwixt Maven in addition to ANT tool.
That's all guys, lots of Java Interview questions? isn't it? I am certainly if yous tin reply this listing of Java questions yous tin easily crevice whatever centre Java or advanced Java interview. Though I receive got non included questions from Java EE or J2EE topics e.g. Servlet, JSP, JSF, JPA, JMS, EJB or whatever other Java EE technology scientific discipline or from major spider web frameworks similar Spring MVC, Struts 2.0, Hibernate or both SOAP in addition to RESTful spider web services, it's nevertheless useful for Java developers preparing for Java spider web developer position, because every Java interview starts alongside questions from fundamentals in addition to JDK API. If yous think, I receive got missed whatever pop Java query hither in addition to yous think it should endure inwards this listing in addition to so experience gratuitous to advise me. My destination is to create the best listing of Java Interview Questions alongside latest in addition to greatest query from recent interviews.
Further Learning
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Sumber https://javarevisited.blogspot.com/
Time is changing in addition to so is Java interviews. Gone are the days, when knowing the divergence betwixt String in addition to StringBuffer tin aid yous to travel past times away through the 2nd circular of interview, questions are becoming to a greater extent than advanced in addition to interviewers are asking to a greater extent than deep questions. When I started my career, questions similar Vector vs Array and HashMap vs Hashtable were the most pop ones in addition to only memorizing them gives yous a goodness adventure to do good inwards interviews, but non anymore. Nowadays, yous volition acquire questions from the areas where non many Java programmer looks e.g. NIO, patterns, sophisticated unit of measurement testing or those which are hard to original e.g. concurrency, algorithms, information structures in addition to coding.
Since I similar to explore interview questions, I receive got got this huge listing of questions alongside me, which contains lots in addition to lots of questions on unlike topics. I receive got been preparing this MEGA listing for quite some fourth dimension in addition to at nowadays It's cook to portion alongside yous guys.
It contains interview questions non solely from classic topics similar threads, collections, equals in addition to hashcode, sockets but also from NIO, array, string, Java 8 in addition to much more.
It has questions for both entry-level Java programmers in addition to senior developers alongside years of experience. No affair whether yous are a Java developer of 1, 2, 3, 4, 5, 6, 8, nine or fifty-fifty 10 years of experience, yous volition uncovering something interesting inwards this list. It contains questions which are super piece of cake to answer, in addition to also, a query which is tricky plenty for fifty-fifty seasoned Java programmers. If yous demand to a greater extent than questions in addition to so yous tin also cheque out this Java Interview Guide: 200+ Interview Questions alongside Answers
Given the listing is long in addition to nosotros receive got questions from everywhere, it's imperative that answers must endure short, concise in addition to crisp, no fluffing at all. So apart from this paragraph, yous volition solely listen from me is the questions in addition to answers, no to a greater extent than context, no to a greater extent than feedback in addition to no to a greater extent than evaluation.
For that, I receive got already written spider web log posts, where yous tin uncovering my views on a particular question, e.g. why I similar that question, what makes them challenging in addition to what form of reply yous should hold back from candidates.
This listing is a piffling flake unlike in addition to I encourage yous to portion questions in addition to answers inwards a similar way so that it should endure piece of cake to revise. I promise this listing tin endure a slap-up usage for both interviewer in addition to candidates, the interviewer can, of course, position a piffling diverseness on questions to convey novelty in addition to surprise element, which is of import for a goodness interview. While a candidate, tin expand in addition to testify their noesis nigh key areas of Java programming linguistic communication in addition to platform.
In 2018 in addition to inwards coming years the focus volition endure to a greater extent than on advanced concurrency concept, JVM internals, 32-bit vs 64-bit JVM, unit of measurement testing, in addition to create clean code. I am sure, i time yous read through this MEGA listing of Java interview question, yous should endure able to do good on both telephonic in addition to human face upward to human face upward programming interviews.
Important Topics for Java Interviews
Apart from quantity, every bit yous tin run across alongside a huge number of questions, I receive got worked hard to maintain character every bit well. I receive got non solely shared questions from all of import topics but also ensured to include so-called advanced topics which many programmers do non prefer to ready or only left out because they receive got non worked on that.Java NIO in addition to JVM internals questions are best examples of that. You tin hold blueprint patterns also on the same listing but growing number of an experienced programmer are at nowadays good aware of GOF blueprint patterns in addition to when to usage them. I receive got also worked hard to hold this listing up-to-date to include what interviewers are asking inwards 2018 in addition to what volition endure their centre focus on coming years. To give yous an idea, this listing of Java interview questions includes next topics:
- Multithreading, concurrency in addition to thread basics
- Date type conversion in addition to fundamentals
- Garbage Collection
- Java Collections Framework
- Array
- String
- GOF Design Patterns
- SOLID blueprint principles
- Abstract shape in addition to interface
- Java basics e.g. equals() in addition to hashcode
- Generics in addition to Enum
- Java IO in addition to NIO
- Common Networking protocols
- Data construction in addition to algorithm inwards Java
- Regular expressions
- JVM internals
- Java Best Practices
- JDBC
- Date, Time, in addition to Calendar
- XML Processing inwards Java
- JUnit
- Programming
You guys are also lucky that nowadays in that location are some goodness books available to ready for Java interviews, i of them which I especially uncovering useful in addition to interesting to read is Java Programming Interview Exposed past times Markham. It volition take yous to some of the most of import topics for Java in addition to JEE interviews, worth reading fifty-fifty if yous are non preparing for Java interview.
Top 120 Java Interview Questions Answers
So at nowadays the fourth dimension has come upward to innovate yous to this MEGA listing of 120 Java questions collected from diverse interviews of in conclusion five years. I am certainly yous receive got seen many of these questions personally on your interviews in addition to many of yous would receive got answered them correctly every bit well.Multithreading, Concurrency in addition to Thread basics Questions
1) Can nosotros brand array volatile inwards Java?
This is i of the tricky Java multi-threading questions yous volition run across inwards senior Java developer Interview. Yes, yous tin brand an array volatile inwards Java but solely the reference which is pointing to an array, non the whole array. What I mean, if i thread changes the reference variable to points to some other array, that volition render a volatile guarantee, but if multiple threads are changing private array elements they won't endure having happens earlier guarantee provided past times the volatile modifier.
2) Can volatile brand a non-atomic performance to atomic?
This some other goodness query I honey to inquire on volatile, mostly every bit a follow-up of the previous question. This query is also non piece of cake to reply because volatile is non nigh atomicity, but in that location are cases where yous tin usage a volatile variable to brand the performance atomic.
One illustration I receive got seen is having a long patch inwards your class. If yous know that a long patch is accessed past times to a greater extent than than i thread e.g. a counter, a cost patch or anything, yous ameliorate travel past times away far volatile. Why? because reading to a long variable is non atomic inwards Java in addition to done inwards ii steps, If i thread is writing or updating long value, it's possible for some other thread to run across one-half value (fist 32-bit). While reading/writing a volatile long or double (64 bit) is atomic.
3) What are practical uses of volatile modifier?
One of the practical usage of the volatile variable is to brand reading double in addition to long atomic. Both double in addition to long are 64-bit broad in addition to they are read inwards ii parts, commencement 32-bit commencement fourth dimension in addition to adjacent 32-bit 2nd time, which is non-atomic but volatile double in addition to long read is atomic inwards Java. Another usage of the volatile variable is to render a retentiveness barrier, only similar it is used inwards Disrupter framework. Basically, Java Memory model inserts a write barrier after yous write to a volatile variable in addition to a read barrier earlier yous read it. Which means, if yous write to volatile patch in addition to so it's guaranteed that whatever thread accessing that variable volition run across the value yous wrote in addition to anything yous did earlier doing that right into the thread is guaranteed to receive got happened in addition to whatever updated information values volition also endure visible to all threads, because the retentiveness barrier flushed all other writes to the cache.
4) What guarantee volatile variable provides? (answer)
volatile variables render the guarantee nigh ordering in addition to visibility e.g. volatile assignment cannot endure re-ordered alongside other statements but inwards the absence of whatever synchronization didactics compiler, JVM or JIT are gratuitous to reorder statements for ameliorate performance. volatile also provides the happens-before guarantee which ensures changes made inwards i thread is visible to others. In some cases volatile also render atomicity e.g. reading 64-bit information types similar long in addition to double are non atomic but read of volatile double or long is atomic.
5) Which i would endure piece of cake to write? synchronization code for 10 threads or 2 threads?
In damage of writing code, both volition endure of same complexity because synchronization code is independent of a number of threads. Choice of synchronization though depends upon a number of threads because the number of thread nowadays to a greater extent than contention, so yous travel past times away for advanced synchronization technique e.g. lock stripping, which requires to a greater extent than complex code in addition to expertise.
6) How do yous telephone phone wait() method? using if block or loop? Why? (answer)
wait() method should ever endure called inwards loop because it's possible that until thread gets CPU to start running i time again the status mightiness non hold, so it's ever ameliorate to cheque status inwards loop earlier proceeding. Here is the criterion idiom of using hold back in addition to notify method inwards Java:
// The criterion idiom for using the hold back method synchronized (obj) { while (condition does non hold) obj.wait(); // (Releases lock, in addition to reacquires on wakeup) ... // Perform activity appropriate to condition }See Effective Java Item 69 to larn to a greater extent than nigh why hold back method should telephone phone inwards the loop.
7) What is imitation sharing inwards the context of multi-threading?
imitation sharing is i of the well-known performance issues on multi-core systems, where each procedure has its local cache. imitation sharing occurs when threads on unlike processor modify variables that reside on same cache delineate every bit shown inwards the next image:
False sharing is real hard to uncovering because the thread may endure accessing completely unlike global variables that tumble out to endure relatively closed together inwards memory. Like many concurrency issues, the primary way to avoid imitation sharing is careful code review in addition to aligning your information construction alongside the size of a cache line.
8) What is busy spin? Why should yous usage it?
Busy spin is i of the technique to hold back for events without releasing CPU. It's often done to avoid losing information inwards CPU cached which is lost if the thread is paused in addition to resumed inwards some other core. So, if yous are working on depression latency arrangement where your guild processing thread currently doesn't receive got whatever order, instead of sleeping or calling wait(), yous tin only loop in addition to and so i time again cheque the queue for novel messages. It's solely beneficial if yous demand to hold back for a real small-scale amount of fourth dimension e.g. inwards micro seconds or nano seconds. LMAX Disrupter framework, a high-performance inter-thread messaging library has a BusySpinWaitStrategy which is based on this concept in addition to uses a busy spin loop for EventProcessors waiting on the barrier.
9) How do yous take thread dump inwards Java?
You tin take a thread dump of Java application inwards Linux past times using kill -3 PID, where PID is the procedure id of Java process. In Windows, yous tin press Ctrl + Break. This volition instruct JVM to impress thread dump inwards criterion out or err in addition to it could travel past times away to console or log file depending upon your application configuration. If yous receive got used Tomcat in addition to so when
10) is Swing thread-safe? (answer)
No, Swing is non thread-safe. You cannot update Swing components e.g. JTable, JList or JPanel from whatever thread, inwards fact, they must endure updated from GUI or AWT thread. That's why swings render invokeAndWait() in addition to invokeLater() method to asking GUI update from whatever other threads. This methods position update asking inwards AWT threads queue in addition to tin hold back till update or render straightaway for an asynchronous update. You tin also cheque the detailed reply to larn more.
11) What is a thread local variable inwards Java? (answer)
Thread-local variables are variables confined to a thread, its similar thread's ain re-create which is non shared betwixt multiple threads. Java provides a ThreadLocal shape to back upward thread-local variables. It's i of the many ways to attain thread-safety. Though endure careful spell using thread local variable inwards manged surround e.g. alongside spider web servers where worker thread out lives whatever application variable. Any thread local variable which is non removed i time its piece of work is done tin potentially drive a retentiveness leak inwards Java application.
12) Write wait-notify code for producer-consumer problem? (answer)
Please run across the reply for a code example. Just recall to telephone phone wait() in addition to notify() method from synchronized block in addition to testify waiting for status on the loop instead of if block.
13) Write code for thread-safe Singleton inwards Java? (answer)
Please run across the reply for a code illustration in addition to stair past times stair guide to creating thread-safe singleton shape inwards Java. When nosotros say thread-safe, which agency Singleton should stay singleton fifty-fifty if initialization occurs inwards the illustration of multiple threads. Using Java enum every bit Singleton shape is i of the easiest ways to create a thread-safe singleton inwards Java.
14) The divergence betwixt slumber in addition to hold back inwards Java? (answer)
Though both are used to suspension currently running thread, sleep() is genuinely meant for brusk suspension because it doesn't release lock, spell wait() is meant for conditional hold back in addition to that's why it release lock which tin in addition to so endure acquired past times some other thread to alter the status on which it is waiting.
15) What is an immutable object? How do yous create an Immutable object inwards Java? (answer)
Immutable objects are those whose state cannot endure changed i time created. Any modification volition number inwards a novel object e.g. String, Integer, and other wrapper class. Please run across the reply for stair past times stair guide to creating Immutable shape inwards Java.
16) Can nosotros create an Immutable object, which contains a mutable object?
Yes, its possible to create an Immutable object which may incorporate a mutable object, yous only demand to endure a piffling flake careful non to portion the reference of the mutable component, instead, yous should render a re-create of it if yous receive got to. Most mutual illustration is an Object which incorporate the reference of java.util.Date object.
Date types in addition to Basic Java Interview Questions
17) What is the right information type to correspond a cost inwards Java? (answer)
BigDecimal if retentiveness is non a delineate of piece of work concern in addition to Performance is non critical, otherwise double alongside predefined precision.
18) How do yous convert bytes to String? (answer)
yous tin convert bytes to the string using string constructor which accepts byte[], only brand certainly that right grapheme encoding otherwise platform's default grapheme encoding volition endure used which may or may non endure same.
19) How do yous convert bytes to long inwards Java? (answer)
This questions if for yous to reply :-)
20) Can nosotros cast an int value into byte variable? what volition tumble out if the value of int is larger than byte?
Yes, nosotros tin cast but int is 32 flake long inwards coffee spell byte is 8 flake long inwards coffee so when yous cast an int to byte higher 24 bits are lost in addition to a byte tin solely concur a value from -128 to 128.
21) There are ii classes B extends H5N1 in addition to C extends B, Can nosotros cast B into C e.g. C = (C) B; (answer)
22) Which shape contains clone method? Cloneable or Object? (answer)
java.lang.Cloneable is marking interface in addition to doesn't incorporate whatever method clone method is defined inwards the object class. It is also knowing that clone() is a native method agency it's implemented inwards C or C++ or whatever other native language.
23) Is ++ operator is thread-safe inwards Java? (answer)
No it's non a thread condom operator because its involve multiple instructions similar reading a value, incriminating it in addition to storing it dorsum into retentiveness which tin endure overlapped betwixt multiple threads.
24) Difference betwixt a = a + b in addition to a += b ? (answer)
The += operator implicitly cast the number of add-on into the type of variable used to concur the result. When yous add together ii integral variable e.g. variable of type byte, short, or int in addition to so they are commencement promoted to int in addition to them add-on happens. If number of add-on is to a greater extent than than maximum value of a in addition to so a + b volition give compile fourth dimension fault but a += b volition endure ok every bit shown below
byte a = 127; byte b = 127; b = a + b; // fault : cannot convert from int to byte b += a; // ok
25) Can I shop a double value inwards a long variable without casting? (answer)
No, yous cannot shop a double value into a long variable without casting because the attain of double is to a greater extent than that long in addition to yous nosotros demand to type cast. It's non dificult to reply this query but many develoepr acquire it wrong due to confusion on which i is bigger betwixt double in addition to long inwards Java.
26) What volition this render 3*0.1 == 0.3? truthful or false? (answer)
This is i of the genuinely tricky questions. Out of 100, solely five developers answered this query in addition to solely of them receive got explained the concept correctly. The brusk reply is imitation because some floating dot numbers tin non endure represented exactly.
27) Which i volition take to a greater extent than memory, an int or Integer? (answer)
An Integer object volition take to a greater extent than retentiveness an Integer is the an object in addition to it store meta information overhead nigh the object in addition to int is primitive type so its takes less space.
28) Why is String Immutable inwards Java? (answer)
One of my favorite Java interview question. The String is Immutable inwards coffee because coffee designer thought that string volition endure heavily used in addition to making it immutable allow some optimization piece of cake sharing same String object betwixt multiple clients. See the link for the to a greater extent than detailed answer. This is a slap-up query for Java programmers alongside less experience every bit it gives them nutrient for thought, to think nigh how things industrial plant inwards Java, what Jave designers mightiness receive got thought when they created String shape etc.
29) Can nosotros usage String inwards the switch case? (answer)
Yes from Java vii onward nosotros tin usage String inwards switch illustration but it is only syntactic sugar. Internally string hash code is used for the switch. See the detaiedl reply for to a greater extent than explanation in addition to discussion.
30) What is constructor chaining inwards Java? (answer)
When yous telephone phone i constructor from other than it's known every bit constructor chaining inwards Java. This happens when yous receive got multiple, overloaded constructor inwards the class.
JVM Internals in addition to Garbage Collection Interview Questions
In the twelvemonth 2018 I receive got seen increased focus on JVM internal in addition to Garbage collection tuning, monitoring Java appliation, dealing alongside Java performance issues on diverse Java interviews. This is genuinely acquire the prime number theme for interviewing whatever experienced Java developer for senior seat e.g. technical lead, VP or squad lead. If yous experience yous are brusk of experience in addition to noesis inwards this surface area in addition to so yous should read atleast i mass mentioned inwards my listing of Java Performance books. I vote goes to Java Performance, The Definitive guide past times Scott.31) What is the size of int inwards 64-bit JVM?
The size of an int variable is constant inwards Java, it's ever 32-bit irrespective of platform. Which agency the size of primitive int is same inwards both 32-bit in addition to 64-bit Java virtual machine.
32) The divergence betwixt Serial in addition to Parallel Garbage Collector? (answer)
Even though both the series in addition to parallel collectors drive a stop-the-world suspension during Garbage collection. The chief divergence betwixt them is that a series collector is a default copying collector which uses solely i GC thread for garbage collection spell a parallel collector uses multiple GC threads for garbage collection.
33) What is the size of an int variable inwards 32-bit in addition to 64-bit JVM? (answer)
The size of int is same inwards both 32-bit in addition to 64-bit JVM, it's ever 32 bits or 4 bytes.
34) H5N1 divergence betwixt WeakReference in addition to SoftReference inwards Java? (answer)
Though both WeakReference in addition to SoftReference helps garbage collector in addition to retentiveness efficient, WeakReference becomes eligible for garbage collection every bit presently every bit in conclusion strong reference is lost but SoftReference fifty-fifty thought it tin non foreclose GC, it tin delay it until JVM absolutely demand memory.
35) How do WeakHashMap works? (answer)
WeakHashMap industrial plant similar a normal HashMap but uses WeakReference for keys, which agency if the key object doesn't receive got whatever reference in addition to so both key/value mapping volition acquire eligible for garbage collection.
36) What is -XX:+UseCompressedOops JVM option? Why usage it? (answer)
When yous travel past times away migrate your Java application from 32-bit to 64-bit JVM, the heap requirement all of a abrupt increases, almost double, due to increasing size of ordinary object pointer from 32 flake to 64 bit. This also adversely deport on how much information yous tin hold inwards CPU cache, which is much smaller than memory. Since chief motivation for moving to 64-bit JVM is to specify large heap size, yous tin salve some retentiveness past times using compressed OOP. By using -XX:+UseCompressedOops, JVM uses 32-bit OOP instead of 64-bit OOP.
37) How do yous uncovering if JVM is 32-bit or 64-bit from Java Program? (answer)
You tin uncovering that past times checking some arrangement properties like sun.arch.data.model or os.arch
38) What is the maximum heap size of 32-bit in addition to 64-bit JVM? (answer)
Theoretically, the maximum heap retentiveness yous tin assign to a 32-bit JVM is 2^32 which is 4GB but practically the bound is much smaller. It also varies betwixt operating systems e.g. shape 1.5GB inwards Windows to almost 3GB inwards Solaris. 64-bit JVM allows yous to specify larger heap size, theoretically 2^64 which is quite large but practically yous tin specify heap infinite upward to 100GBs. There are fifty-fifty JVM e.g. Azul where heap infinite of M gigs is also possible.
39) What is the divergence betwixt JRE, JDK, JVM in addition to JIT? (answer)
JRE stands for Java run-time in addition to it's required to run Java application. JDK stands for Java evolution kit in addition to provides tools to prepare Java computer program e.g. Java compiler. It also contains JRE. The JVM stands for Java virtual machine in addition to it's the procedure responsible for running Java application. The JIT stands for Just In Time compilation in addition to helps to boost the performance of Java application past times converting Java byte code into native code when the crossed certainly threshold i.e. mainly hot code is converted into native code.
40) Explain Java Heap infinite in addition to Garbage collection? (answer)
When a Java procedure is started using coffee command, retentiveness is allocated to it. Part of this retentiveness is used to create heap space, which is used to allocate retentiveness to objects whenever they are created inwards the program. Garbage collection is the procedure within JVM which reclaims retentiveness from dead objects for futurity allocation.
41) Can yous guarantee the garbage collection process? (answer)
No, yous cannot guarantee the garbage collection, though yous tin brand a asking using System.gc() or Runtime.gc() method.
42) How do yous uncovering retentiveness usage from Java program? How much pct of the heap is used?
You tin usage retentiveness related methods from java.lang.Runtime shape to acquire the gratuitous memory, total retentiveness in addition to maximum heap retentiveness inwards Java. By using these methods, yous tin uncovering out how many percents of the heap is used in addition to how much heap infinite is remaining. Runtime.freeMemory() render amount of gratuitous retentiveness inwards bytes, Runtime.totalMemory() returns total retentiveness inwards bytes in addition to Runtime.maxMemory() returns maximum retentiveness inwards bytes.
43) What is the divergence betwixt stack in addition to heap inwards Java? (answer)
Stack in addition to heap are unlike retentiveness areas inwards the JVM in addition to they are used for unlike purposes. The stack is used to concur method frames in addition to local variables spell objects are ever allocated retentiveness from the heap. The stack is ordinarily much smaller than heap retentiveness in addition to also didn't shared betwixt multiple threads, but heap is shared amid all threads inwards JVM.
Basic Java concepts Interview Questions
44) What's the divergence betwixt "a == b" in addition to "a.equals(b)"? (answer)The a = b does object reference matching if both a in addition to b are an object in addition to solely render truthful if both are pointing to the same object inwards the heap space, on the other hand, a.equals(b) is used for logical mapping in addition to its expected from an object to override this method to render logical equality. For example, String shape overrides this equals() method so that yous tin compare ii Strings, which are the unlike object but contains same letters.
45) What is a.hashCode() used for? How is it related to a.equals(b)? (answer)
hashCode() method returns an int hash value corresponding to an object. It's used inwards hash based collection classes e.g Hashtable, HashMap, LinkedHashMap in addition to so on. It's real tightly related to equals() method. According to Java specification, ii objects which are equal to each other using equals() method must receive got same hash code.
46) Difference betwixt final, finalize in addition to finally? (answer)
The concluding is a modifier which yous tin apply to variable, methods in addition to classes. If yous brand a variable concluding it agency its value cannot endure changed i time initialized. finalize is a method, which is called only earlier an object is a garbage collected, giving it in conclusion adventure to resurrect itself, but the telephone phone to finalize is non guaranteed. finally is a keyword which is used inwards exception treatment along alongside attempt in addition to catch. the finally block is ever executed irrespective of whether an exception is thrown from attempt block or not.
47) What is a compile fourth dimension constant inwards Java? What is the endangerment of using it?
world static concluding variables are also known every bit a compile fourth dimension constant, earth is optional there. They are replaced alongside actual values at compile fourth dimension because compiler know their value up-front in addition to also knows that it cannot endure changed during run-time. One of the occupation alongside this is that if yous happened to usage a world static concluding variable from some in-house or 3rd political party library in addition to their value changed after than your customer volition nevertheless endure using erstwhile value fifty-fifty after yous deploy a novel version of JARs. To avoid that, brand certainly yous compile your computer program when yous upgrade dependency JAR files.
Java Collections Framework Interview Questions
It also contains Data construction in addition to algorithm Interview query inwards Java, questions on array, linked list, HashMap, ArrayList, Hashtable, Stack, Queue, PriorityQueue, LinkedHashMap in addition to ConcurrentHashMap.48) The divergence betwixt List, Set, Map, in addition to Queue inwards Java? (answer)
The listing is an ordered collection which allows duplicate. It also has an implementation which provides constant fourth dimension index based access, but that is non guaranteed past times List interface. Set is unordered collection which
49) Difference betwixt poll() in addition to remove() method?
Both poll() in addition to remove() take out the object from the Queue but if poll() fails in addition to so it returns zero but if take away fails it throws Exception.
50) The divergence betwixt LinkedHashMap in addition to PriorityQueue inwards Java? (answer)
PriorityQueue guarantees that lowest or highest priority chemical element ever stay at the caput of the queue, but LinkedHashMap maintains the guild on which elements are inserted. When yous iterate over a PriorityQueue, iterator doesn't guarantee whatever guild but iterator of LinkedHashMap does guarantee the guild on which elements are inserted.
51) Difference betwixt ArrayList in addition to LinkedList inwards Java? (answer)
The obvious divergence betwixt them is that ArrrayList is backed past times array information structure, supprots random access in addition to LinkedList is backed past times linked listing information construction in addition to doesn't supprot random access. Accessing an chemical element alongside the index is O(1) inwards ArrayList but its O(n) inwards LinkedList. See the reply for to a greater extent than detailed discussion.
52) What is a duad of ways that yous could sort a collection? (answer)
You tin either usage the Sorted collection similar TreeSet or TreeMap or yous tin sort using the ordered collection similar a listing in addition to using Collections.sort() method.
53) How do yous impress Array inwards Java? (answer)
You tin impress an array past times using the Arrays.toString() in addition to Arrays.deepToString() method. Since array doesn't implement toString() past times itself, only passing an array to System.out.println() volition non impress its contents but Arrays.toString() volition impress each element.
54) LinkedList inwards Java is doubly or singly linked list? (answer)
It's a doubly linked list, yous tin cheque the code inwards JDK. In Eclipse, yous tin usage the shortcut, Ctrl + T to straight opened upward this shape inwards Editor.
55) Which form of tree is used to implement TreeMap inwards Java? (answer)
H5N1 Red Black tree is used to implement TreeMap inwards Java.
56) What is the divergence betwixt Hashtable in addition to HashMap? (answer)It's a doubly linked list, yous tin cheque the code inwards JDK. In Eclipse, yous tin usage the shortcut, Ctrl + T to straight opened upward this shape inwards Editor.
55) Which form of tree is used to implement TreeMap inwards Java? (answer)
H5N1 Red Black tree is used to implement TreeMap inwards Java.
There are many differences betwixt these ii classes, some of them are following:
a) Hashtable is a legacy shape in addition to nowadays from JDK 1, HashMap was added later.
b) Hashtable is synchronized in addition to slower but HashMap is non synchronized in addition to faster.
c) Hashtable doesn't allow zero keys but HashMap allows i zero key.
See the reply for to a greater extent than differences betwixt HashMap in addition to Hashtable inwards Java.
57) How HashSet industrial plant internally inwards Java? (answer)
HashSet is internally implemented using an HashMap. Since a Map needs key in addition to value, a default value is used for all keys. Similar to HashMap, HashSet doesn't allow duplicate keys in addition to solely i zero key, I hateful yous tin solely shop i zero object inwards HashSet.
58) Write code to take away elements from ArrayList spell iterating? (answer)
Key hither is to cheque whether candidate uses ArrayList's remove() or Iterator's remove(). Here is the sample code which uses right way o take away elements from ArrayList spell looping over in addition to avoids ConcurrentModificationException.
59) Can I write my ain container shape in addition to usage it inwards the for-each loop?
Yes, yous tin write your ain container class. You demand to implement the Iterable interface if yous desire to loop over advanced for loop inwards Java, though. If yous implement Collection in addition to so yous past times default acquire that property.
60) What is default size of ArrayList in addition to HashMap inwards Java? (answer)
As of Java vii now, default size of ArrayList is 10 in addition to default capacity of HashMap is 16, it must endure powerfulness of 2. Here is code snippet from ArrayList and HashMap shape :
// from ArrayList.java JDK 1.7 private static final int DEFAULT_CAPACITY = 10; //from HashMap.java JDK 7 static final int DEFAULT_INITIAL_CAPACITY = 1 << 4; // aka 16
61) Is it possible for ii unequal objects to receive got the same hashcode?
Yes, ii unequal objects tin receive got same hashcode that's why collision tumble out inwards a hashmap.
the equal hashcode contract solely says that ii equal objects must receive got the same hashcode it doesn't say anything nigh the unequal object.
62) Can ii equal object receive got the unlike hash code?
No, thats non possible according to hash code contract.
63) Can nosotros usage random numbers inwards the hashcode() method? (answer)
No, because hashcode of an object should endure ever same. See the reply to learning to a greater extent than nigh things to recall spell overriding hashCode() method inwards Java.
64) What is the divergence betwixt Comparator in addition to Comparable inwards Java? (answer)
The Comparable interface is used to define the natural guild of object spell Comparator is used to define custom order. Comparable tin endure ever one, but nosotros tin receive got multiple comparators to define customized guild for objects.
65) Why yous demand to override hashcode, when yous override equals inwards Java? (answer)
Because equals receive got code contract mandates to override equals in addition to hashcode together .since many container shape similar HashMap or HashSet depends on hashcode in addition to equals contract.
Java IO in addition to NIO Interview questions
IO is real of import from Java interview dot of view. You should receive got a goodness noesis of erstwhile Java IO, NIO, in addition to NIO2 alsong alongside some operating arrangement in addition to disk IO fundamentals. Here are some oftentimes asked questions shape Java IO.66) In my Java program, I receive got 3 sockets? How many threads I volition demand to grip that?
67) How do yous create ByteBuffer inwards Java?
68) How do yous write in addition to read from ByteBuffer inwards Java?
69) Is Java BIG endian or LITTLE endian?
70) What is the byte guild of ByteBuffer?
71) The divergence betwixt direct buffer in addition to non-direct buffer inwards Java? (answer)
72) What is the retentiveness mapped buffer inwards Java? (answer)
73) What is TCP NO DELAY socket option?
74) What is the divergence betwixt TCP in addition to UDP protocol? (answer)
75) The divergence betwixt ByteBuffer in addition to StringBuffer inwards Java? (answer)
Java Best Practices Interview question
Contains best practices from unlike parts of Java programming e.g. Collections, String, IO, Multi-threading, Error in addition to Exception handling, blueprint patterns etc. This department is mostly for experience Java developer, technical lead, AVP, squad atomic number 82 in addition to coders who are responsible for products. If yous desire to create character products yous must know in addition to follow the best practices.76) What best practices yous follow spell writing multi-threaded code inwards Java? (answer)
Here are duad of best practices which I follow spell writing concurrent code inwards Java:
a) Always squall your thread, this volition aid inwards debugging.
b) minimize the orbit of synchronization, instead of making whole method synchronized, solely critical department should endure synchronized.
c) prefer volatile over synchronized if yous tin can.
e) usage higher aeroplane concurrency utilities instead of waitn() in addition to notify for inter thread communication e.g. BlockingQueue, CountDownLatch in addition to Semeaphore.
e) Prefer concurrent collection over synchronized collection inwards Java. They render ameliorate scalability.
77) Tell me few best practices yous apply spell using Collections inwards Java? (answer)
Here are duad of best practices I follow spell using Collectionc classes from Java:
a) Always usage the right collection e.g. if yous demand non-synchronized listing in addition to so usage ArrayList in addition to non Vector.
b) Prefer concurrent collection over synchronized collection because they are to a greater extent than scalable.
c) Always usage interface to a correspond in addition to access a collection e.g. usage List to shop ArrayList, Map to shop HashMap in addition to so on.
d) Use iterator to loop over collection.
e) Always usage generics alongside collection.
78) Can yous tell us at to the lowest degree five best practise yous usage spell using threads inwards Java? (answer)
This is similar to the previous query in addition to yous tin usage the reply given there. Particularly alongside thread, yous should:
a) squall your thread
b) hold your task in addition to thread separate, usage Runnable or Callable alongside thread puddle executor.
c) usage thread pool
d) usage volatile to betoken compiler nigh ordering, visibility, in addition to atomicity.
e) avoid thread local variable because wrong usage of ThreadLocal shape inwards Java tin create a retentiveness leak.
Look in that location are many best practices in addition to I give extra points to the developer which convey something new, something fifty-fifty I don't know. I brand certainly to inquire this query to Java developers of 8 to 10 years of experience only to justice his hands on experience in addition to knowledge.
79) Name five IO best practices? (answer)
IO is real of import for performance of your Java application. Ideally yous should avoid IO inwards critical path of your application. Here are duad of Java IO best practices yous tin follow:
a) Use buffered IO classes instead of reading private bytes in addition to char.
b) Use classes from NIO in addition to NIO2
c) Always closed streams inwards finally block or usage try-with-resource statements.
d) usage retentiveness mapped file for faster IO.
If a Java candidate doesn't know nigh IO in addition to NIO, especially if he has at least 2 to 4 years of experience, he needs some reading.80) Name five JDBC best practices your follow? (answer)
Another goodness Java best practices for experienced Java developer of vii to 8 years experience. Why it's important? because they are the ones which laid the tendency inwards the code in addition to educate junior developers. There are many best practices in addition to yous tin squall every bit per your confort in addition to conviniece. Here are some of the to a greater extent than mutual ones:
a) usage batch declaration for inserting in addition to updating data.
b) usage PreparedStatement to avoid SQL exception in addition to ameliorate performance.
c) usage database connectedness pool
d) access resultset using column squall instead of column indexes.
e) Don't generate dynamic SQL past times concatenating String alongside user input.
81) Name duad of method overloading best practices inwards Java? (answer)
Here are some best practices yous tin follow spell overloading a method inwards Java to avoid confusion alongside auto-boxing:
a) Don't overload method where i accepts int in addition to other accepts Integer.
b) Don't overload method where number of declaration is same in addition to solely guild of declaration is different.
c) Use varargs after overloaded methods has to a greater extent than than five arguments.
Date, Time in addition to Calendar Interview questions inwards Java
82) Does SimpleDateFormat is condom to usage inwards the multi-threaded program? (answer)
No, unfortunately, DateFormat in addition to all its implementations including SimpleDateFormat is non thread-safe, so should non endure used inwards the multi-threaded computer program until external thread-safety measures are applied e.g. confining SimpleDateFormat object into a ThreadLocal variable. If yous don't do that, yous volition acquire an wrong number spell parsing or formatting dates inwards Java. Though, for all practical appointment fourth dimension purpose, I highly recommend joda-time library.
83) How do yous format a appointment inwards Java? e.g. inwards the ddMMyyyy format? (answer)
You tin either usage SimpleDateFormat shape or joda-time library to format appointment inwards Java. DateFormat shape allows yous to format appointment on many pop formats. Please run across the reply for code samples to format appointment into unlike formats e.g. dd-MM-yyyy or ddMMyyyy.
84) How do yous demo timezone inwards formatted appointment inwards Java? (answer)
85) The divergence betwixt java.util.Date in addition to java.sql.Date inwards Java? (answer)
86) How to yous calculate the divergence betwixt ii dates inwards Java? (program)
87) How do yous convert a String(YYYYMMDD) to appointment inwards Java? (answer)
Unit testing JUnit Interview questions
89) How do yous testify static method? (answer)You tin usage PowerMock library to testify static methods inwards Java.
90) How to do yous testify a method for an exception using JUnit? (answer)
91) Which unit of measurement testing libraries yous receive got used for testing Java programs? (answer)
92) What is the divergence betwixt @Before in addition to @BeforeClass annotation? (answer)
Programming in addition to Coding Questions
93) How to cheque if a String contains solely numeric digits? (solution)94) How to write LRU cache inwards Java using Generics? (answer)
95) Write a Java computer program to convert bytes to long? (answer)
96) How to contrary a String inwards Java without using StringBuffer? (solution)
98) How do yous cheque if ii given String are anagrams? (solution)
99) How to impress all permutation of a String inwards Java? (solution)
100) How do yous impress duplicate elements from an array inwards Java? (solution)
101) How to convert String to int inwards Java? (solution)
102) How to swap ii integers without using temp variable? (solution)
Java Interview questions from OOP in addition to Design Patterns
It contains Java Interview questions from SOLID blueprint principles, OOP fundamentals e.g. class, object, interface, Inheritance, Polymorphism, Encapsulation, in addition to Abstraction every bit good every bit to a greater extent than advanced concepts similar Composition, Aggregation, in addition to Association. It also contains questions from GOF blueprint patterns.103) What is the interface? Why yous usage it if yous cannot write anything concrete on it?
The interface is used to define API. It tells nigh the contract your classes volition follow. It also supports abstraction because a customer tin usage interface method to leverage multiple implementations e.g. past times using List interface yous tin take wages of random access of ArrayList every bit good every bit flexible insertion in addition to deletion of LinkedList. The interface doesn't allow yous to write code to hold things abstract but from Java 8 yous tin declare static in addition to default methods within interface which are concrete.
104) The divergence betwixt abstract shape in addition to interface inwards Java? (answer)
There are multiple differences betwixt abstract shape in addition to interface inwards Java, but the most of import i is Java's restriction on allowing a shape to extend only i shape but allows it to implement multiple interfaces. An abstract shape is goodness to define default conduct for a solid unit of measurement of class, but the interface is goodness to define Type which is after used to leverage Polymorphism. Please cheque the reply for a to a greater extent than thorough give-and-take of this question.
105) Which blueprint pattern receive got yous used inwards your production code? apart from Singleton?
This is something yous tin reply from your experience. You tin to a greater extent than often than non say nigh dependency injection, mill pattern, decorator pattern or observer pattern, whichever yous receive got used. Though endure prepared to reply follow-up query based upon the pattern yous choose.
106) Can yous explicate Liskov Substitution principle? (answer)
This is i of the toughest questions I receive got asked inwards Java interviews. Out of 50 candidates, I receive got almost asked solely five receive got managed to reply it. I am non posting an reply to this query every bit I similar yous to do some research, practise in addition to pass some fourth dimension to sympathize this confusing regulation well.
107) What is Law of Demeter violation? Why it matters? (answer)
Believe it or not, Java is all nigh application programming in addition to structuring code. If you receive got goodness noesis of common coding best practices, patterns in addition to what non to do than solely yous tin write character code. Law of Demeter suggests yous "talk to friends in addition to non stranger", so used to cut down coupling betwixt classes.
108) What is Adapter pattern? When to usage it?
Another oftentimes asked Java blueprint pattern questions. It provides interface conversion. If your customer is using some interface but yous receive got something else, yous tin write an Adapter to span them together. This is goodness for Java software engineer having 2 to 3 years experience because the query is neither hard nor tricky but requires noesis of OOP blueprint patterns.
109) What is "dependency injection" in addition to "inversion of control"? Why would someone usage it? (answer)
110) What is an abstract class? How is it unlike from an interface? Why would yous usage it? (answer)
One to a greater extent than classic query from Programming Job interviews, it is every bit erstwhile every bit chuck Norris. An abstract shape is a shape which tin receive got state, code in addition to implementation, but an interface is a contract which is totally abstract. Since I receive got answered it many times, I am solely giving yous the gist hither but yous should read the article linked to reply to larn this useful concept inwards much to a greater extent than detail.
111) Which i is ameliorate constructor injection or setter dependency injection? (answer)
Each has their ain wages in addition to disadvantage. Constructor injection guaranteed that shape volition endure initialized alongside all its dependency, but setter injection provides flexibility to laid an optional dependency. Setter injection is also to a greater extent than readable if yous are using an XML file to pull dependency. Rule of pollex is to usage constructor injection for mandatory dependency in addition to usage setter injection for optional dependency.
112) What is divergence betwixt dependency injection in addition to mill blueprint pattern? (answer)
Though both patterns aid to take out object creation component division from application logic, usage of dependency injection results inwards cleaner code than mill pattern. By using dependency injection, your classes are cipher but POJO which solely knows nigh dependency but doesn't tending how they are acquired. In the illustration of mill pattern, the shape also needs to know nigh mill to acquire dependency. hence, DI results inwards to a greater extent than testable classes than mill pattern. Please run across the reply for a to a greater extent than detailed give-and-take on this topic.
113) Difference betwixt Adapter in addition to Decorator pattern? (answer)
Though the construction of Adapter in addition to Decorator pattern is similar, the divergence comes on the intent of each pattern. The adapter pattern is used to span the gap betwixt ii interfaces, but Decorator pattern is used to add together novel functionality into the shape without the modifying existing code.
114) Difference betwixt Adapter in addition to Proxy Pattern? (answer)
Similar to the previous question, the divergence betwixt Adapter in addition to Proxy patterns is inwards their intent. Since both Adapter in addition to Proxy pattern encapsulate the shape which genuinely does the job, so number inwards the same structure, but Adapter pattern is used for interface conversion spell the Proxy pattern is used to add together an extra aeroplane of indirection to back upward distribute, controlled or intelligent access.
115) What is Template method pattern? (answer)
Template pattern provides an outline of an algorithm in addition to lets yous configure or customize its steps. For examples, yous tin persuasion a sorting algorithm every bit a template to sort object. It defines steps for sorting but permit yous configure how to compare them using Comparable or something similar inwards some other language. The method which outlines the algorithms is also known every bit template method.
116) When do yous usage Visitor blueprint pattern? (answer)
The visitor pattern is a solution of occupation where yous demand to add together performance on a shape hierarchy but without touching them. This pattern uses double dispatch to add together some other aeroplane of indirection.
117) When do yous usage Composite blueprint pattern? (answer)
Composite blueprint pattern arranges objects into tree structures to correspond part-whole hierarchies. It allows clients care for private objects in addition to container of objects uniformly. Use Composite pattern when yous desire to correspond part-whole hierarchies of objects.
118) The divergence betwixt Inheritance in addition to Composition? (answer)
Though both allows code reuse, Composition is to a greater extent than flexible than Inheritance because it allows yous to switch to some other implementation at run-time. Code written using Composition is also easier to testify than code involving inheritance hierarchies.
119) Describe overloading in addition to overriding inwards Java? (answer)
Both overloading in addition to overriding allow yous to write ii methods of unlike functionality but alongside the same name, but overloading is compile fourth dimension activity spell overriding is run-time activity. Though yous tin overload a method inwards the same class, but yous tin solely override a method inwards tyke classes. Inheritance is necessary for overriding.
120) The divergence betwixt nested world static shape in addition to a top aeroplane shape inwards Java? (answer)
You tin receive got to a greater extent than than i nested world static shape within i class, but yous tin solely receive got i top-level world shape inwards a Java rootage file in addition to its squall must endure same every bit the squall of Java rootage file.
121) Difference betwixt Composition, Aggregation in addition to Association inwards OOP? (answer)
If ii objects are related to each other, they are said to endure associated alongside each other. Composition in addition to Aggregation are ii forms of association inwards object-oriented programming. The composition is stronger association than Aggregation. In Composition, i object is OWNER of some other object spell inwards Aggregation i object is only USER of some other object. If an object H5N1 is composed of object B in addition to so B doesn't be if H5N1 ceased to exists, but if object H5N1 is only an aggregation of object B in addition to so B tin exists fifty-fifty if H5N1 ceased to exist.
122) Give me an illustration of blueprint pattern which is based upon opened upward closed principle? (answer)
This is i of the practical questions I inquire experienced Java programmer. I hold back them to know nigh OOP blueprint principles every bit good every bit patterns. Open closed blueprint regulation asserts that your code should endure opened upward for extension but closed for modification. Which agency if yous desire to add together novel functionality, yous tin add together it easily using the novel code but without touching already tried in addition to tested code. There are several blueprint patterns which are based upon opened upward closed blueprint regulation e.g. Strategy pattern if yous demand a novel strategy, only implement the interface in addition to configure, no demand to modify centre logic. One working illustration is Collections.sort() method which is based on Strategy pattern in addition to follows the open-closed principle, yous don't modify sort() method to sort a novel object, what yous do is only implement Comparator inwards your ain way.
123) Difference betwixt Abstract mill in addition to Prototype blueprint pattern? (answer)
This is the practise query for you, If yous are feeling bored only reading in addition to itching to write something, why non write the reply to this question. I would honey to run across an illustration the, which should reply where yous should usage the Abstract mill pattern in addition to where is the Prototype pattern is to a greater extent than suitable.
124) When do yous usage Flyweight pattern? (answer)
This is some other pop query from the blueprint pattern. Many Java developers alongside 4 to half-dozen years of experience know the Definition but failed to give whatever concrete example. Since many of yous mightiness non receive got used this pattern, it's ameliorate to appear examples from JDK. You are to a greater extent than probable receive got used them earlier in addition to they are piece of cake to recall every bit well. Now let's run across the answer.
Flyweight pattern allows yous to portion object to back upward large numbers without genuinely creating likewise many objects. In guild to use Flyweight pattern, yous demand to brand your object Immutable so that they tin endure safely shared. String puddle in addition to puddle of Integer in addition to Long object inwards JDK are goodness examples of Flyweight pattern.
Miscellaneous Java Interview Questions
It contains XML Processing inwards Java Interview question, JDBC Interview question, Regular expressions Interview questions, Java Error in addition to Exception Interview Questions, Serialization,125) The divergence betwixt nested static shape in addition to top aeroplane class? (answer)
One of the telephone substitution questions from Java basics. I inquire this query solely to junior Java developers of 1 to 2 years of experience every bit it's likewise piece of cake for an experience Java programmers. The reply is simple, a world top aeroplane shape must receive got the same squall every bit the squall of the rootage file, in that location is no such requirement for nested static class. H5N1 nested shape is ever within a top aeroplane shape in addition to yous demand to usage the squall of the top-level shape to refer nested static shape e.g. HashMap.Entry is a nested static class, where HashMap is a top aeroplane shape in addition to Entry is nested static class.
126) Can yous write a regular facial expression to cheque if String is a number? (solution)
If yous are taking Java interviews in addition to so yous should inquire at to the lowest degree i query on the regular expression. This clearly differentiates an average programmer alongside a goodness programmer. Since i of the traits of a goodness developer is to know tools, regex is the best tool for searching something inwards the log file, preparing reports etc. Anyway, reply to this query is, a numeric String tin solely incorporate digits i.e. 0 to nine and + in addition to - sign that likewise at start of the String, past times using this information yous tin write next regular facial expression to cheque if given String is number or not
127) The divergence betwixt checked in addition to unchecked Exception inwards Java? (answer)
checked exception is checked past times the compiler at compile time. It's mandatory for a method to either grip the checked exception or declare them inwards their throws clause. These are the ones which are a sub shape of Exception but doesn't descend from RuntimeException. The unchecked exception is the descendant of RuntimeException in addition to non checked past times the compiler at compile time. This query is at nowadays becoming less pop in addition to yous would solely uncovering this alongside interviews alongside small-scale companies, both investment banks in addition to startups are moved on from this question.
128) The divergence betwixt throw in addition to throws inwards Java? (answer)
the throw is used to genuinely throw an instance of java.lang.Throwable class, which agency yous tin throw both Error in addition to Exception using throw keyword e.g.
throw new IllegalArgumentException("size must endure multiple of 2")
On the other hand, throws is used every bit component division of method annunciation in addition to signals which form of exceptions are thrown past times this method so that its caller tin grip them. It's mandatory to declare whatever unhandled checked exception inwards throws clause inwards Java. Like the previous question, this is some other oftentimes asked Java interview query from errors in addition to exception theme but likewise piece of cake to answer.
129) The divergence betwixt Serializable in addition to Externalizable inwards Java? (answer)
This is i of the oftentimes asked questions from Java Serialization. The interviewer has been asking this query since the twenty-four threescore minutes menstruum Serialization was introduced inwards Java, but yet solely a few goodness candidate tin reply this query alongside some confidence in addition to practical knowledge. Serializable interface is used to brand Java classes serializable so that they tin endure transferred over network or their state tin endure saved on disk, but it leverages default serialization built-in JVM, which is expensive, delicate in addition to non secure. Externalizable allows yous to fully command the Serialization process, specify a custom binary format in addition to add together to a greater extent than security measure.
130) The divergence betwixt DOM in addition to SAX parser inwards Java? (answer)
Another mutual Java query but from XML parsing topic. It's rather uncomplicated to reply in addition to that's why many interviewers prefers to inquire this query on the telephonic round. DOM parser loads the whole XML into retentiveness to create a tree based DOM model which helps it apace locate nodes in addition to brand a alter inwards the construction of XML spell SAX parser is an trial based parser in addition to doesn't charge the whole XML into memory. Due to this argue DOM is faster than SAX but require to a greater extent than retentiveness in addition to non suitable to parse large XML files.
131) Tell me 3 features introduced on JDK 1.7? (answer)
This is i of the goodness questions I inquire to cheque whether the candidate is aware of recent evolution inwards Java technology scientific discipline infinite or not. Even though JDK vii was non a large bang release similar JDK five or JDK 8, it nevertheless has a lot of goodness characteristic to count on e.g. try-with-resource statements, which gratuitous yous from closing streams in addition to resources when yous are done alongside that, Java automatically closes that. Fork-Join puddle to implement something similar the Map-reduce pattern inwards Java. Allowing String variable in addition to literal into switch statements. Diamond operator for improved type inference, no demand to declare generic type on the right-hand side of variable annunciation anymore, results inwards to a greater extent than readable in addition to succinct code. Another worth noting characteristic introduced was improved exception treatment e.g. allowing yous to grab multiple exceptions inwards the same grab block.
132) Tell me five features introduced inwards JDK 1.8? (answer)
This is the follow-up query of the previous one. Java 8 is path breaking release inwards Java's history, hither are the top five features from JDK 8 release
- Lambda expression, which allows yous travel past times an anonymous role every bit object.
- Stream API, take wages of multiple cores of modern CPU in addition to allows yous to write succinct code.
- Date in addition to Time API, finally yous receive got a solid in addition to piece of cake to usage appointment in addition to fourth dimension library right into JDK
- Extension methods, at nowadays yous tin receive got static in addition to default method into your interface
- Repeated annotation, allows yous apply the same notation multiple times on a type
133) What is the divergence betwixt Maven in addition to ANT inwards Java? (answer)
Another slap-up query to cheque the all circular noesis of Java developers. It's piece of cake to reply questions from centre Java but when yous inquire nigh setting things up, edifice Java artifacts, many Java software engineer struggles. Coming dorsum to the reply of this question, Though both are build tool in addition to used to create Java application build, Maven is much to a greater extent than than that. It provides criterion construction for Java projection based upon "convention over configuration" concept in addition to automatically care dependencies (JAR files on which your application is dependent) for Java application. Please run across the reply for to a greater extent than differences betwixt Maven in addition to ANT tool.
That's all guys, lots of Java Interview questions? isn't it? I am certainly if yous tin reply this listing of Java questions yous tin easily crevice whatever centre Java or advanced Java interview. Though I receive got non included questions from Java EE or J2EE topics e.g. Servlet, JSP, JSF, JPA, JMS, EJB or whatever other Java EE technology scientific discipline or from major spider web frameworks similar Spring MVC, Struts 2.0, Hibernate or both SOAP in addition to RESTful spider web services, it's nevertheless useful for Java developers preparing for Java spider web developer position, because every Java interview starts alongside questions from fundamentals in addition to JDK API. If yous think, I receive got missed whatever pop Java query hither in addition to yous think it should endure inwards this listing in addition to so experience gratuitous to advise me. My destination is to create the best listing of Java Interview Questions alongside latest in addition to greatest query from recent interviews.
Further Learning
Complete Java Masterclass
see here)
Recommended Books for Java Programmers
If yous are looking for some goods to ready for your Java Interviews, You tin take a appear at next books to embrace both theory in addition to coding questions:
- nine Must Read Books for Java Developers (see book)
- five Java Performance Tuning Books for Experienced Programmers (see book)
- five Good Books for Java JEE Interviews (see book)
- five Books to larn Data Structure in addition to Algorithms (see book)
- five Hibernate Books for Java Developers (see book)
- five Spring Books for Java Developers (see book)
References
- The Java Virtual Machine Spefication (see here)
- The Java linguistic communication Specification (Java SE 8) (see here)
- Java SE 8 API Specification (see here)
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