10 Singleton Blueprint Interview Questions Inwards Coffee - Answered
Thursday, September 6, 2018
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Singleton pattern pattern is i of the most mutual patterns you lot volition run across inwards Java applications together with it’s too used heavily inwards heart Java libraries. Questions from Singleton pattern is really mutual inwards Java interviews together with proficient cognition of how to implement Singleton pattern sure help.This is too i of my favorite design pattern interview question together with has lots of interesting follow-up to dig into details , this non exclusively cheque the cognition of pattern pattern but too cheque coding, multithreading facial expression which is really of import patch working for a existent life application. In this post service conduct maintain listed but about of the most mutual inquiry asked on Singleton pattern during a Java Interview. I conduct maintain non provided the answers of these questions every bit they are easily available via google search but if you lot guys demand I tin dismiss endeavor to modify this tutorial to include answers every bit well.
As promised before together with having received lot of asking for providing answers of these question, I conduct maintain decided to update this post service along amongst answers. By the agency if you lot are preparing for interview on Java applied scientific discipline than you lot tin dismiss cheque my collection on Java interview questions together with multi-threading interview questions.
There are lot of resources inwards which tin dismiss aid you lot inwards your interview preparation. On the other manus if you lot are to a greater extent than interested on pattern pattern tutorials than you lot tin dismiss cheque my post service on builder pattern pattern
Answer : Any course of report which you lot desire to last available to whole application together with whole exclusively i lawsuit is feasible is candidate of becoming Singleton. One instance of this is Runtime course of report , since on whole coffee application exclusively i runtime surroundings tin dismiss last possible making Runtime Singleton is correct decision. Another instance is a utility classes similar Popup inwards GUI application, if you lot desire to present popup amongst message you lot tin dismiss conduct maintain i PopUp course of report on whole GUI application together with anytime but acquire its instance, together with telephone band show() amongst message.
Answer : Until asked don’t write code using double checked locking every bit it is to a greater extent than complex together with chances of errors are to a greater extent than but if you lot conduct maintain deep cognition of double checked locking, volatile variable together with lazy loading than this is your run a endangerment to shine. I conduct maintain shared code examples of writing singleton classes using enum, using static manufacturing works life together with amongst double checked locking inwards my recent post service Why Enum Singletons are improve inwards Java, delight run across there.
Double checked locking should exclusively last used when you lot conduct maintain requirement for lazy initialization otherwise use Enum to implement singleton or unproblematic static concluding variable.
Answer : Preferred agency is non to implement Cloneable interface every bit why should i wants to do clone() of Singleton together with if you lot do but throw Exception from clone() method every bit “Can non do clone of Singleton class”.
Answer: This is similar to previous interview question. Since constructor of Singleton course of report is supposed to last mortal it prevents creating lawsuit of Singleton from exterior but Reflection tin dismiss access mortal fields together with methods, which opens a threat of but about other instance. This tin dismiss last avoided past times throwing Exception from constructor every bit “Singleton already initialized”
Answer: You tin dismiss forestall this past times using readResolve() method, since during serialization readObject() is used to do lawsuit together with it render novel lawsuit every fourth dimension but past times using readResolve you lot tin dismiss supervene upon it amongst master Singleton instance. I conduct maintain shared code on how to do it inwards my post service Enum every bit Singleton inwards Java. This is too i of the argue I conduct maintain said that purpose Enum to do Singleton because serialization of enum is taken attention past times JVM together with it provides guaranteed of that.
Apart from these questions on Singleton pattern, but about of my reader contribute few to a greater extent than questions, which I included here. Thank you lot guys for your contribution.
Sumber https://javarevisited.blogspot.com/
As promised before together with having received lot of asking for providing answers of these question, I conduct maintain decided to update this post service along amongst answers. By the agency if you lot are preparing for interview on Java applied scientific discipline than you lot tin dismiss cheque my collection on Java interview questions together with multi-threading interview questions.
There are lot of resources inwards which tin dismiss aid you lot inwards your interview preparation. On the other manus if you lot are to a greater extent than interested on pattern pattern tutorials than you lot tin dismiss cheque my post service on builder pattern pattern
10 Interview inquiry on Singleton Pattern inwards Java
Here is my collection of interview questions based upon Singleton pattern pattern. They are collected from diverse Java interviews together with highlights cardinal aspects of pattern together with where it is broken, if you lot know how to do thread-safe singletons together with unlike ways to implement this pattern, together with pros together with cons of each approach. Questions starts amongst :What is Singleton class? Have you lot used Singleton before?
Singleton is a course of report which has exclusively i lawsuit inwards whole application together with provides a getInstance() method to access the singleton instance. There are many classes inwards JDK which is implemented using Singleton pattern similar java.lang.Runtime which provides getRuntime() method to acquire access of it together with used to acquire free retentivity together with full retentivity inwards Java.Which classes are candidates of Singleton? Which form of course of report do you lot brand Singleton inwards Java?
Here they cheque whether candidate has plenty sense on usage of singleton or not. Does he is familiar of advantage/disadvantage or alternatives available for singleton inwards Java or not.Answer : Any course of report which you lot desire to last available to whole application together with whole exclusively i lawsuit is feasible is candidate of becoming Singleton. One instance of this is Runtime course of report , since on whole coffee application exclusively i runtime surroundings tin dismiss last possible making Runtime Singleton is correct decision. Another instance is a utility classes similar Popup inwards GUI application, if you lot desire to present popup amongst message you lot tin dismiss conduct maintain i PopUp course of report on whole GUI application together with anytime but acquire its instance, together with telephone band show() amongst message.
Can you lot write code for getInstance() method of a Singleton course of report inwards Java?
Most of the coffee programmer neglect hither if they conduct maintain mugged upwardly the singleton code because you lot tin dismiss inquire lots of follow-up inquiry based upon the code they conduct maintain written. I conduct maintain seen many programmer write Singleton getInstance() method amongst double checked locking but they are non actually familiar amongst the caveat associated amongst double checking of singleton prior to Java 5.Answer : Until asked don’t write code using double checked locking every bit it is to a greater extent than complex together with chances of errors are to a greater extent than but if you lot conduct maintain deep cognition of double checked locking, volatile variable together with lazy loading than this is your run a endangerment to shine. I conduct maintain shared code examples of writing singleton classes using enum, using static manufacturing works life together with amongst double checked locking inwards my recent post service Why Enum Singletons are improve inwards Java, delight run across there.
Is it improve to brand whole getInstance() method synchronized or but critical department is enough? Which i you lot volition prefer?
This is actually prissy inquiry together with I mostly asked to but rapidly cheque whether candidate is aware of functioning merchandise off of unnecessary locking or not. Since locking exclusively brand sense when nosotros demand to do lawsuit together with residue of the fourth dimension its but read exclusively access hence locking of critical department is ever improve option. read to a greater extent than most synchronization on How Synchronization works inwards Java Answer : This is over again related to double checked locking pattern, good synchronization is costly together with when you lot apply this on whole method than telephone band to getInstance() volition last synchronized together with contented. Since synchronization is exclusively needed during initialization on singleton instance, to forestall creating but about other lawsuit of Singleton, It’s improve to exclusively synchronize critical department together with non whole method. Singleton pattern is too closely related to factory pattern pattern where getInstance() serves every bit static manufacturing works life method.
Answer : As in that place are many ways to implement Singleton similar using double checked locking or Singleton course of report amongst static final lawsuit initialized during course of report loading. Former is called lazy loading because Singleton lawsuit is created exclusively when customer calls getInstance() method patch afterwards is called early on loading because Singleton lawsuit is created when course of report is loaded into memory.
What is lazy together with early on loading of Singleton together with how volition you lot implement it?
This is but about other slap-up Singleton interview inquiry inwards terms of agreement of concept of loading together with terms associated amongst course of report loading inwards Java. Many of which I conduct maintain interviewed non actually familiar amongst this but its proficient to know concept.Answer : As in that place are many ways to implement Singleton similar using double checked locking or Singleton course of report amongst static final lawsuit initialized during course of report loading. Former is called lazy loading because Singleton lawsuit is created exclusively when customer calls getInstance() method patch afterwards is called early on loading because Singleton lawsuit is created when course of report is loaded into memory.
Give me but about examples of Singleton pattern from Java Development Kit?
This is opened upwardly inquiry to all, delight part which classes are Singleton inwards JDK. Answer to this inquiry is java.lang.Runtime Answer : There are many classes inwards Java Development Kit which is written using singleton pattern, hither are few of them:
Answer : Double checked locking is a technique to forestall creating but about other lawsuit of Singleton when telephone band to getInstance() method is made inwards multi-threading environment. In Double checked locking pattern every bit shown inwards below example, singleton lawsuit is checked ii times before initialization. See here to larn to a greater extent than most double-checked-locking inwards Java.
- Java.lang.Runtime amongst getRuntime() method
- Java.awt.Toolkit amongst getDefaultToolkit()
- Java.awt.Desktop amongst getDesktop()
What is double checked locking inwards Singleton?
One of the most hyped inquiry on Singleton pattern together with actually demands consummate agreement to acquire it correct because of Java Memory model caveat prior to Java 5. If a guy comes upwardly amongst a solution of using volatile keyword amongst Singleton lawsuit together with explains it hence it actually shows it has inwards depth cognition of Java retentivity model together with he is constantly updating his Java knowledge.Answer : Double checked locking is a technique to forestall creating but about other lawsuit of Singleton when telephone band to getInstance() method is made inwards multi-threading environment. In Double checked locking pattern every bit shown inwards below example, singleton lawsuit is checked ii times before initialization. See here to larn to a greater extent than most double-checked-locking inwards Java.
public static Singleton getInstance(){ if(_INSTANCE == null){ synchronized(Singleton.class){ //double checked locking - because minute cheque of Singleton lawsuit amongst lock if(_INSTANCE == null){ _INSTANCE = new Singleton(); } } } return _INSTANCE; }
Double checked locking should exclusively last used when you lot conduct maintain requirement for lazy initialization otherwise use Enum to implement singleton or unproblematic static concluding variable.
How do you lot forestall for creating but about other lawsuit of Singleton using clone() method?
This type of questions mostly comes but about fourth dimension past times asking how to interruption singleton or when Singleton is non Singleton inwards Java.Answer : Preferred agency is non to implement Cloneable interface every bit why should i wants to do clone() of Singleton together with if you lot do but throw Exception from clone() method every bit “Can non do clone of Singleton class”.
How do you lot forestall for creating but about other lawsuit of Singleton using reflection?
Open to all. In my catch throwing exception from constructor is an option.Answer: This is similar to previous interview question. Since constructor of Singleton course of report is supposed to last mortal it prevents creating lawsuit of Singleton from exterior but Reflection tin dismiss access mortal fields together with methods, which opens a threat of but about other instance. This tin dismiss last avoided past times throwing Exception from constructor every bit “Singleton already initialized”
How do you lot forestall for creating but about other lawsuit of Singleton during serialization?
Another slap-up inquiry which requires cognition of Serialization inwards Java and how to purpose it for persisting Singleton classes. This is opened upwardly to you lot all but inwards my catch purpose of readResolve() method tin dismiss sort this out for you.Answer: You tin dismiss forestall this past times using readResolve() method, since during serialization readObject() is used to do lawsuit together with it render novel lawsuit every fourth dimension but past times using readResolve you lot tin dismiss supervene upon it amongst master Singleton instance. I conduct maintain shared code on how to do it inwards my post service Enum every bit Singleton inwards Java. This is too i of the argue I conduct maintain said that purpose Enum to do Singleton because serialization of enum is taken attention past times JVM together with it provides guaranteed of that.
When is Singleton non a Singleton inwards Java?
There is a really proficient article introduce inwards Sun's Java site which discusses diverse scenarios when a Singleton is non actually remains Singleton together with multiple lawsuit of Singleton is possible. Here is the link of that article http://java.sun.com/developer/technicalArticles/Programming/singletons/Apart from these questions on Singleton pattern, but about of my reader contribute few to a greater extent than questions, which I included here. Thank you lot guys for your contribution.
Why you lot should avoid the singleton anti-pattern at all together with supervene upon it amongst DI?
Answer : Singleton Dependency Injection: every course of report that needs access to a singleton gets the object through its constructors or amongst a DI-container.Why Singleton is Anti pattern
With to a greater extent than together with to a greater extent than classes calling getInstance() the code gets to a greater extent than together with to a greater extent than tightly coupled, monolithic, non testable together with difficult to alter together with difficult to reuse because of non configurable, hidden dependencies. Also, in that place would last no demand for this clumsy double checked locking if you lot telephone band getInstance less oftentimes (i.e. once).
How many ways you lot tin dismiss write Singleton Class inwards Java?
Answer : I know at to the lowest degree 4 ways to implement Singleton pattern inwards Java- Singleton past times synchronizing getInstance() method
- Singleton amongst world static concluding land initialized during course of report loading.
- Singleton generated past times static nested class, too referred every bit Singleton holder pattern.
- From Java v on-wards using Enums
How to write thread-safe Singleton inwards Java?
Answer : Thread security Singleton ordinarily refers to write thread security code which creates i together with exclusively i lawsuit of Singleton if called past times multiple thread at same time. There are many ways to laissez passer on this similar past times using double checked locking technique every bit shown inwards a higher house together with past times using Enum or Singleton initialized past times course of report loader. At in conclusion few to a greater extent than questions for your practice, contributed past times Mansi, Thank you lot Mansi
14) Singleton vs Static Class?
15) When to select Singleton over Static Class?
16) Can you lot supervene upon Singleton amongst Static Class inwards Java?
17) Difference betwixt Singleton together with Static Class inwards java?
18) Advantage of Singleton over Static Class?
I conduct maintain covered answers of pair of these questions inwards my post, Singleton vs Static Class inwards Java - Pros together with Cons. If you lot similar to read to a greater extent than Java interview questions you lot tin dismiss conduct maintain a await on but about of my favorites below
Further Learning
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50+ Programmer Phone Interview Questions amongst answers (more)
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Java Programming Interview Exposed
Cracking the Coding Interview: 150 Programming Questions
14) Singleton vs Static Class?
15) When to select Singleton over Static Class?
16) Can you lot supervene upon Singleton amongst Static Class inwards Java?
17) Difference betwixt Singleton together with Static Class inwards java?
18) Advantage of Singleton over Static Class?
I conduct maintain covered answers of pair of these questions inwards my post, Singleton vs Static Class inwards Java - Pros together with Cons. If you lot similar to read to a greater extent than Java interview questions you lot tin dismiss conduct maintain a await on but about of my favorites below
Further Learning
questions)
50+ Java Mulithreading Questions from Last iii years (questions)
50+ Programmer Phone Interview Questions amongst answers (more)
Recommended Books
Java Programming Interview Exposed
Cracking the Coding Interview: 150 Programming Questions
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