10 Garbage Collection Interview Questions Too Answers Inwards Coffee Programming

GC Interview Questions Answer inward Java

Garbage collection interview questions are really pop inward both essence Java together with advanced Java Interviews. Apart from  Java Collection together with Thread  many tricky Java questions stems Garbage collections which are tough to answer. In this Java Interview article I volition part to a greater extent than or less questions from GC which is asked inward 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 together with tuning. As I said GC is an of import business office of whatever Java interview together with then brand certain you lot receive got proficient command inward GC. One to a greater extent than affair which is getting really of import is mightiness to covert together with understand Garbage collection Output, to a greater extent than together with to a greater extent than interviewer are checking whether candidate tin move empathise GC output or not. During Java interview they may supply a snippet of GC output together with inquire diverse questions based on that e.g. Which Garbage collector is used, whether output is from major collection or little fry collection, How much retentiveness is gratuitous from GC, What is size of novel generation together with erstwhile generation later on GC etc. I receive got included few Garbage collection interview questions together with answers from GC output to aid alongside that. It’s recommended to railroad train questions from Java collection,  multithreading together with programming along alongside Garbage collection to create good inward Java interviews at whatever stage.

Interview questions on Java Garbage collection

Here is to a greater extent than or less Garbage collection Interview questions from my personal collection, which I receive got created from my sense together with alongside the aid of diverse friends together with colleagues which has shared GC interview questions alongside me. Actually at that spot are lot many questions than What I am sharing hither but to proceed this ship service little I idea to solely part to a greater extent than or less questions, I tin move recall of minute business office of GC interview query if you lot guys discovery this useful.

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

Answer : In lodge to ameliorate perform inward Garbage collection questions inward whatever Java interview, It’s of import to receive got basic agreement of  Java Heap space. To larn to a greater extent than close heap, encounter my post 10 points on Java heap space. By the way Heap is divided into dissimilar generation e.g. novel generation, erstwhile generation together with PermGen space.PermGen infinite is used to shop class’s metadata together with filling of PermGen infinite tin move cause java.lang.OutOfMemory:PermGen space. Its also worth noting to remember JVM pick to configure PermGen space inward Java.

Question 2 - How create you lot position little fry together with major garbage collection inward Java?

Answer: Minor collection prints “GC” if garbage collection logging is enable using –verbose:gc or -XX:PrintGCDetails, spell Major collection prints “Full GC”. This Garbage collection interview query is based on agreement of Garbage collection output. As to a greater extent than together with to a greater extent than Interviewer are asking query to depository fiscal establishment friction match candidate’s mightiness to empathise GC output, this theme buy the farm fifty-fifty to a greater extent than important.

Question iii - What is divergence betwixt ParNew together with DefNew Young Generation Garbage collector?

Answer : This Garbage Collection interview questions is latterly asked to i of my friend. It require to a greater extent than than average cognition on GC to respond this question. By the way ParNew together with DefNew is 2 immature generation garbage collector. ParNew is a multi-threaded GC used along alongside concurrent Mark Sweep spell DefNew is unmarried threaded GC used along alongside Serial Garbage Collector.

Question four - How create you lot discovery GC resulted due to calling System.gc()?

Answer : Another GC interview query which is based on GC output. Similar to major together with little fry collection, at that spot volition live on a give-and-take “System” included inward Garbage collection output.

Question five - What is divergence betwixt Serial together with Throughput Garbage collector?

Answer : Serial Garbage collector is a halt the basis GC which stops application thread from running during both minor together with major collection. Serial Garbage collector tin move live on enabled using JVM pick -XX:UseSerialGC together with it's designed for Java application which doesn't receive got intermission fourth dimension requirement together with receive got customer configuration. Serial Garbage collector was also default GC inward JDK 1.4 earlier ergonomics was introduced inward 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 paw Throughput garbage collector is parallel collector where little fry together with major collection happens inward parallel taking sum wages of all the organization resources available similar multiple processor. Though both major together with little fry collection runs on stop-the-world fashion together with introduced intermission inward application. Throughput Garbage collector tin move live on enable using -XX:UseParallelGC or -XX:UseOldParallelGC. It increases overall throughput of application my minimizing fourth dimension spent inward Garbage collection but however has long pauses during sum GC.This is a sort of Garbage collection interview questions which gives you lot an chance to demo your cognition inward especial spell answering. I e'er advise to respond these sort of questions inward detail.  See Java Performance The Definitive Guide for to a greater extent than details on this topic.

Question vi – When does an Object becomes eligible for Garbage collection inward Java ?

Answer : An object becomes eligible for garbage collection when at that spot is no alive reference for that object or it tin move non live on reached past times whatever alive thread. Cyclic reference doesn’t count equally alive reference together with if 2 objects are pointing to each other together with at that spot is no alive reference for whatever of them, than both are eligible for GC. Also Garbage collection thread is a daemon thread which volition run past times JVM based upon GC algorithm together with when runs it collects all objects which are eligible for GC.

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

Answer : Finalize method inward Java also called finalizer is a method defined inward java.lang.Object together with called past times Garbage collector earlier collecting whatever object which is eligible for GC. Finalize() method provides in conclusion gamble to object to create cleanup together with gratuitous whatever remaining resource, to larn to a greater extent than close finalizers, read What is finalize method inward Java.

Question 8 - If Object Influenza A virus subtype H5N1 has reference to Object B together with Object B refer to Object A, apart from that at that spot 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 buy the farm eligible for Garbage collection”. An object becomes eligible for Garbage collection if at that spot is no alive reference for it. It tin move non live on accessible from whatever Thread together with cyclic dependency doesn’t foreclose Object from beingness Garbage collected. Which agency inward this instance both Object Influenza A virus subtype H5N1 together with Object B are eligible of Garbage collection. See How Garbage collection plant inward Java for more details.

Question ix -Can nosotros strength Garbage collector to run at whatever fourth dimension ?

Answer : No, you lot tin move non strength Garbage collection inward Java. Though you lot tin move asking it past times calling Sytem.gc() or its cousin Runtime.getRuntime().gc(). It’s non guaranteed that GC volition run right away equally consequence of calling these method.

Question 10 - Does Garbage collection occur inward permanent generation infinite inward 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 together with since it maintains degree Meta information together with String pool, whether its eligible for garbage collection or not. By the way Garbage Collection does occur inward PermGen infinite together with if PermGen infinite is sum or cross a threshold, it tin move trigger Full GC. If you lot hold off at output of GC you lot volition discovery that PermGen infinite is also garbage collected. This is why right sizing of PermGen infinite is of import to avoid frequent sum GC. You tin move command size of PermGen infinite past times JVM options -XX:PermGenSize together with -XX:MaxPermGenSize.

Question xi : How to you lot monitor garbage collection activities?

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

Question 12: Look at below Garbage collection output together with respond 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 together with sum 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 flow Occupancy of Young Generation ?

This Garbage collection Interview questions is completely based on GC output. Following are answers of to a higher house GC questions which volition non solely aid you lot to respond these query but also aid you lot to empathise together with translate GC output.

Answer 1:  It's Minor collection because of "GC" word, In instance of Major collection, you lot would encounter "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 inward bracket is sum size of Young Generation, which include Eden together with 2 survivor space. 1512K on left of arrow is occupancy of Yong Generation earlier GC together with 64K is occupancy later on GC. On the adjacent describe of piece of occupation value if bracket is sum heap size which is (600345K). If nosotros subtract size of immature generation to sum heap size nosotros tin move calculate size of Old Generation. This describe of piece of occupation also shows occupancy of heap earlier together with later on Garbage collection.

Answer 4: As answered inward previous garbage collection interview question, minute describe of piece of occupation shows heap occupancy earlier together with later on Garbage collection. If nosotros subtract value of right side 13569K, to value on left side 15604K, nosotros tin move acquire sum retentiveness freed past times GC.

Answer 5: 0.0636056 secs on minute describe of piece of occupation denotes sum fourth dimension it took to collect dead objects during Garbage collection. It also include fourth dimension taken to GC immature generation which is shown inward starting fourth dimension describe of piece of occupation (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 you lot know the respond than you lot tin move  post via comments.

Question -  What is divergence betwixt -XX:ParallelGC together with -XX:ParallelOldGC?

Question - When create you lot ConcurrentMarkSweep Garbage collector together with Throughput GC?

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

Question -  Have you lot done whatever garbage collection tuning? What was your approach?

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