10 Garbage Collection Interview Questions Together With Answers Inwards Coffee Programming

GC Interview Questions Answer inwards Java

Garbage collection interview questions are rattling pop inwards both essence Java as well as advanced Java Interviews. Apart from  Java Collection as well as Thread  many tricky Java questions stems Garbage collections which are tough to answer. In this Java Interview article I volition part around questions from GC which is asked inwards diverse essence Java interviews.These questions are based upon concept of How Garbage collection works, Different kinds of Garbage collector and JVM parameters used for garbage collection monitoring as well as tuning. As I said GC is an of import business office of whatsoever Java interview then brand certain y'all receive got skillful command inwards GC. One to a greater extent than matter which is getting rattling of import is mightiness to encompass as well as understand Garbage collection Output, to a greater extent than as well as to a greater extent than interviewer are checking whether candidate tin strength out empathize GC output or not. During Java interview they may render a snippet of GC output as well as enquire diverse questions based on that e.g. Which Garbage collector is used, whether output is from major collection or tike collection, How much retentiveness is costless from GC, What is size of novel generation as well as one-time generation afterward GC etc. I receive got included few Garbage collection interview questions as well as answers from GC output to aid alongside that. It’s recommended to create questions from Java collection,  multithreading as well as programming along alongside Garbage collection to produce good inwards Java interviews at whatsoever stage.

Interview questions on Java Garbage collection

Here is around Garbage collection Interview questions from my personal collection, which I receive got created from my sense as well as alongside the aid of diverse friends as well as colleagues which has shared GC interview questions alongside me. Actually in that place are lot many questions than What I am sharing hither but to proceed this transportation service little I idea to solely part around questions, I tin strength out hollo back of minute business office of GC interview query if y'all guys notice this useful.

Question 1 - What is construction of Java Heap ? What is Perm Gen infinite inwards Heap ?

Answer : In guild to improve perform inwards Garbage collection questions inwards whatsoever Java interview, It’s of import to receive got basic agreement of  Java Heap space. To larn to a greater extent than most heap, run across my post 10 points on Java heap space. By the way Heap is divided into unlike generation e.g. novel generation, one-time generation as well as PermGen space.PermGen infinite is used to shop class’s metadata as well as filling of PermGen infinite tin strength out cause java.lang.OutOfMemory:PermGen space. Its also worth noting to remember JVM pick to configure PermGen space inwards Java.

Question 2 - How produce y'all position tike as well as major garbage collection inwards Java?

Answer: Minor collection prints “GC” if garbage collection logging is enable using –verbose:gc or -XX:PrintGCDetails, piece Major collection prints “Full GC”. This Garbage collection interview query is based on agreement of Garbage collection output. As to a greater extent than as well as to a greater extent than Interviewer are asking query to cheque candidate’s mightiness to empathize GC output, this theme acquire fifty-fifty to a greater extent than important.

Question iii - What is divergence betwixt ParNew as well as DefNew Young Generation Garbage collector?

Answer : This Garbage Collection interview questions is lately asked to i of my friend. It require to a greater extent than than average noesis on GC to reply this question. By the way ParNew as well as DefNew is ii immature generation garbage collector. ParNew is a multi-threaded GC used along alongside concurrent Mark Sweep piece DefNew is unmarried threaded GC used along alongside Serial Garbage Collector.

Question four - How produce y'all notice GC resulted due to calling System.gc()?

Answer : Another GC interview query which is based on GC output. Similar to major as well as tike collection, in that place volition live a discussion “System” included inwards Garbage collection output.

Question five - What is divergence betwixt Serial as well as Throughput Garbage collector?

Answer : Serial Garbage collector is a halt the globe GC which stops application thread from running during both minor as well as major collection. Serial Garbage collector tin strength out live enabled using JVM pick -XX:UseSerialGC as well as it's designed for Java application which doesn't receive got recess fourth dimension requirement as well as receive got customer configuration. Serial Garbage collector was also default GC inwards JDK 1.4 earlier ergonomics was introduced inwards JDK 1.5. Serial GC is most suited for little application alongside less number of thread while throughput GG is to a greater extent than suited for large applications. On the other mitt Throughput garbage collector is parallel collector where tike as well as major collection happens inwards parallel taking amount payoff of all the organisation resources available similar multiple processor. Though both major as well as tike collection runs on stop-the-world fashion as well as introduced recess inwards application. Throughput Garbage collector tin strength out live enable using -XX:UseParallelGC or -XX:UseOldParallelGC. It increases overall throughput of application my minimizing fourth dimension spent inwards Garbage collection but all the same has long pauses during amount GC.This is a variety of Garbage collection interview questions which gives y'all an chance to exhibit your noesis inwards exceptional piece answering. I ever propose to reply these variety of questions inwards detail.  See Java Performance The Definitive Guide for to a greater extent than details on this topic.

Question half-dozen – When does an Object becomes eligible for Garbage collection inwards Java ?

Answer : An object becomes eligible for garbage collection when in that place is no alive reference for that object or it tin strength out non live reached yesteryear whatsoever alive thread. Cyclic reference doesn’t count equally alive reference as well as if ii objects are pointing to each other as well as in that place is no alive reference for whatsoever of them, than both are eligible for GC. Also Garbage collection thread is a daemon thread which volition run yesteryear JVM based upon GC algorithm as well as when runs it collects all objects which are eligible for GC.

Question vii - What is finalize method inwards Java ? When does Garbage collector calls finalize method inwards Java ?

Answer : Finalize method inwards Java also called finalizer is a method defined inwards java.lang.Object as well as called yesteryear Garbage collector earlier collecting whatsoever object which is eligible for GC. Finalize() method provides lastly gamble to object to produce cleanup as well as costless whatsoever remaining resource, to larn to a greater extent than most finalizers, read What is finalize method inwards Java.

Question 8 - If Object Influenza A virus subtype H5N1 has reference to Object B as well as Object B refer to Object A, apart from that in that place is no alive reference to either object Influenza A virus subtype H5N1 or B, Does they are eligible to Garbage collection ?

This Garbage collection interview questions is related query five “When object acquire eligible for Garbage collection”. An object becomes eligible for Garbage collection if in that place is no alive reference for it. It tin strength out non live accessible from whatsoever Thread as well as cyclic dependency doesn’t foreclose Object from beingness Garbage collected. Which way inwards this illustration both Object Influenza A virus subtype H5N1 as well as Object B are eligible of Garbage collection. See How Garbage collection plant inwards Java for more details.

Question nine -Can nosotros strength Garbage collector to run at whatsoever fourth dimension ?

Answer : No, y'all tin strength out non strength Garbage collection inwards Java. Though y'all tin strength out asking it yesteryear calling Sytem.gc() or its cousin Runtime.getRuntime().gc(). It’s non guaranteed that GC volition run forthwith equally effect of calling these method.

Question 10 - Does Garbage collection occur inwards permanent generation infinite inwards JVM?

Answer : This  is a tricky Garbage collection interview query equally many programmers are non certain whether PermGen infinite is business office of Java heap space or non as well as since it maintains degree Meta information as well as String pool, whether its eligible for garbage collection or not. By the way Garbage Collection does occur inwards PermGen infinite as well as if PermGen infinite is amount or cross a threshold, it tin strength out trigger Full GC. If y'all await at output of GC y'all volition notice that PermGen infinite is also garbage collected. This is why right sizing of PermGen infinite is of import to avoid frequent amount GC. You tin strength out command size of PermGen infinite yesteryear JVM options -XX:PermGenSize as well as -XX:MaxPermGenSize.

Question eleven : How to y'all monitor garbage collection activities?

Answer : One of my favorite interview questions on Garbage collection, only to check whether candidate has ever monitored GC activities or not. You tin strength out monitor garbage collection activities either offline or real-time. You tin strength out purpose tools similar JConsole as well as VisualVM VM alongside its Visual GC plug-in to monitor existent fourth dimension garbage collection activities as well as retentiveness condition of JVM or y'all tin strength out redirect Garbage collection output to a log file for offline analysis yesteryear using -XlogGC=<PATH> JVM parameter. Anyway y'all should ever enable GC options similar -XX:PrintGCDetails -X:verboseGC as well as -XX:PrintGCTimeStamps equally it doesn't impact application performance much but render useful states for functioning monitoring.

Question 12: Look at below Garbage collection output as well as reply next query :

[GC

       [ParNew: 1512K->64K(1512K), 0.0635032 secs]

       15604K->13569K(600345K), 0.0636056 secs]

       [Times: user=0.03 sys=0.00, real=0.06 secs]

 1. Is this output of Major Collection or Minor Collection ?

 2. Which immature Generation Garbage collector is used ?

 3. What is size of Young Generation, Old Generation as well as amount Heap Size?

 4. How much retentiveness is freed from Garbage collection ?

 5. How much fourth dimension is taken for Garbage collection ?

 6. What is electrical current Occupancy of Young Generation ?

This Garbage collection Interview questions is completely based on GC output. Following are answers of inwards a higher house GC questions which volition non solely aid y'all to reply these query but also aid y'all to empathize as well as translate GC output.

Answer 1:  It's Minor collection because of "GC" word, In illustration of Major collection, y'all would run across "Full GC".

Answer 2: This output is of multi-threaded Young Generation Garbage collector "ParNew", which is used along alongside CMS concurrent Garbage collector.

Answer 3: [1512K] which is written inwards bracket is amount size of Young Generation, which include Eden as well as ii survivor space. 1512K on left of arrow is occupancy of Yong Generation earlier GC as well as 64K is occupancy afterward GC. On the side yesteryear side business value if bracket is amount heap size which is (600345K). If nosotros subtract size of immature generation to amount heap size nosotros tin strength out calculate size of Old Generation. This business also shows occupancy of heap earlier as well as afterward Garbage collection.

Answer 4: As answered inwards previous garbage collection interview question, minute business shows heap occupancy earlier as well as afterward Garbage collection. If nosotros subtract value of right side 13569K, to value on left side 15604K, nosotros tin strength out acquire amount retentiveness freed yesteryear GC.

Answer 5: 0.0636056 secs on minute business denotes amount fourth dimension it took to collect dead objects during Garbage collection. It also include fourth dimension taken to GC immature generation which is shown inwards get-go business (0635032 secs).

Answer 6: 64K 

Here are few to a greater extent than interesting Garbage collection Interview question for your practice, I haven’t provided answers of all garbage collection interview questions. If y'all know the reply than y'all tin strength out  post via comments.

Question -  What is divergence betwixt -XX:ParallelGC as well as -XX:ParallelOldGC?

Question - When produce y'all ConcurrentMarkSweep Garbage collector as well as Throughput GC?

Question -  What is divergence betwixt ConcurrentMarkSweep and G1 garbage collector?

Question -  Have y'all done whatsoever garbage collection tuning? What was your approach?

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