The ultimate guide to Java interviews with 300+ real-world questions and answers. Get interview-ready in just a few hours with strategies developed by FAANG engineers.

It’s very common to have interviews testing your knowledge of a programming language you claim to be an expert in.

If you've got an interview coming up on Java soon and need to get up to speed, this is the ideal course for you. You'll refresh your memory on everything from the basics to more advanced functionality you’re likely to be asked about. Even if you're using Java every day, you may not have been exposed to parts of it in some time, so it's always useful to make sure you're updated.

This course features more than 300 of the most commonly asked core Java interview questions that you're likely to face as an experienced software engineer. You'll get to explore questions by topic, as well as see detailed answers for each one, and plenty of live code examples where relevant. Get started today.

The Java Interview Handbook: 300+ Interview Questions

<div class="card">
   # Question # 1
    <div class="qtn">
        <p>What is a garbage collector?</p>
    </div>
    <div class="ans">
<p>Unlike other languages, Java takes off the load of memory management from the developer. The crux is Java determines what objects are no longer used and reclaims the memory for future use. Java's garbage collection tracks live objects and everything else is assumed to be garbage. Garbage collector is the program running in the background that looks into all the objects in the memory.</p>
<p>Java ships with several garbage collectors. More specifically, these are different algorithms that run in their own threads. Each works differently and has pros and cons. The most important thing to keep in mind is that <span class="hi-yl-b">all garbage collectors stop the world. That is, your application is put on hold or paused, as the garbage is collected and taken out.</span> The main difference among the algorithms is how they stop the world. Some algorithms sit completely idle until the garbage collection is absolutely needed and then pause your application for a long period while others do most of their work concurrently with your application and thus need a shorter pause during stop the world phase. The best algorithm depends on your goals: are you optimizing for throughput where long pauses every now and then are tolerable or you are optimizing for low latency by spreading it out and having short pauses all along.</p>
</div>

</div>


<div class="card">
   # Question # 2
    <div class="qtn">
        <p>Explain the garbage collection process in Java. 
</p>
    </div>
    <div class="ans">
<ul>
        <li><p>Whenever a new object is created, it is allocated its space in the Eden memory. The Eden memory is limited and fills up fast. Initially, both the survivor spaces are empty. Let's call them survivor space A and B to distinguish between them.</p></li>

<li><p> When the garbage collector runs for the first time, it marks alive objects in Eden memory and any unused objects are collected as garbage. The objects surviving the garbage collector run are placed in one of the survivor spaces. For our example let's imagine they are placed in survivor space A.</p></li>

<li><p>On the second run of the GC the surviving objects from the Eden memory and the survivor memory A are placed in the unused survivor memory B.</p></li>

<li><p><span class="hi-yl">The two survivor spaces exist to avoid memory fragmentation. After the GC run is complete on Eden memory and one of the survivor spaces, the two memory spaces will have holes in them since dead objects have been reclaimed. Instead of dealing with compaction, JVM chooses to move all the alive objects over from Eden and the in-use survivor space to the unused survivor space.</span> Avoiding compaction is the reason for having two survivor memory spaces.</p></li>

<li><p>Upon surviving X rounds of garbage collection, where X depends on the JVM implementation,  an object is expected to live forever and gets promoted to the old or tenured generation. Before the promotion, the object ping pongs between the two survivor spaces as GC runs take place.</p></li>

<li><p>Garbage collection runs on tenured generation once it becomes full. However, memory compaction can't be avoided for this memory space and garbage collection takes more time than when it runs on the young generation.</p></li>
</ul>
</div>
</div>


<div>
   # Question # 1
    <div>
        <p>What is a garbage collector?</p>
    </div>
    <div>
<p>Unlike other languages, Java takes off the load of memory management from the developer. The crux is Java determines what objects are no longer used and reclaims the memory for future use. Java's garbage collection tracks live objects and everything else is assumed to be garbage. Garbage collector is the program running in the background that looks into all the objects in the memory.</p>
<p>Java ships with several garbage collectors. More specifically, these are different algorithms that run in their own threads. Each works differently and has pros and cons. The most important thing to keep in mind is that <span>all garbage collectors stop the world. That is, your application is put on hold or paused, as the garbage is collected and taken out.</span> The main difference among the algorithms is how they stop the world. Some algorithms sit completely idle until the garbage collection is absolutely needed and then pause your application for a long period while others do most of their work concurrently with your application and thus need a shorter pause during stop the world phase. The best algorithm depends on your goals: are you optimizing for throughput where long pauses every now and then are tolerable or you are optimizing for low latency by spreading it out and having short pauses all along.</p>
</div>

</div>


<div>
   # Question # 2
    <div>
        <p>Explain the garbage collection process in Java. 
</p>
    </div>
    <div>
<ul>
        <li><p>Whenever a new object is created, it is allocated its space in the Eden memory. The Eden memory is limited and fills up fast. Initially, both the survivor spaces are empty. Let's call them survivor space A and B to distinguish between them.</p></li>

<li><p> When the garbage collector runs for the first time, it marks alive objects in Eden memory and any unused objects are collected as garbage. The objects surviving the garbage collector run are placed in one of the survivor spaces. For our example let's imagine they are placed in survivor space A.</p></li>

<li><p>On the second run of the GC the surviving objects from the Eden memory and the survivor memory A are placed in the unused survivor memory B.</p></li>

<li><p><span>The two survivor spaces exist to avoid memory fragmentation. After the GC run is complete on Eden memory and one of the survivor spaces, the two memory spaces will have holes in them since dead objects have been reclaimed. Instead of dealing with compaction, JVM chooses to move all the alive objects over from Eden and the in-use survivor space to the unused survivor space.</span> Avoiding compaction is the reason for having two survivor memory spaces.</p></li>

<li><p>Upon surviving X rounds of garbage collection, where X depends on the JVM implementation,  an object is expected to live forever and gets promoted to the old or tenured generation. Before the promotion, the object ping pongs between the two survivor spaces as GC runs take place.</p></li>

<li><p>Garbage collection runs on tenured generation once it becomes full. However, memory compaction can't be avoided for this memory space and garbage collection takes more time than when it runs on the young generation.</p></li>
</ul>
</div>
</div>


This lesson explains the working of garbage collection works in Java.

Java Ecosystem

Methods

Classes

Interfaces

Inheritance

Lambda Expressions

Generics

Multi-Threading

Memory Management

Collections

Exceptions

Reflection

Serialization

Miscellaneous Topics

Java in Practice

Patterns

The End

Garbage Collection

Question # 1

Question # 2