Get a leg up on the competition – 10+ Java Interview Questions You Must Prepare In 2022

Interview season has officially begun, so it’s time to get a leg up on the competition by brushing up on your knowledge of the most popular programming languages. 2018 saw Java, Python, C++, C#, and JavaScript top the list of the 10 most in-demand programming languages , so if you want to ace your interview this year (and land that job), then you need to know your stuff when it comes to Java questions . Here are 120+ Java interview questions you must prepare for in 2022, along with my sample answers that’ll make sure you knock your next interview out of the park.

What is an interface?

There are two things to understand about interfaces. The first is that an interface contains only abstract methods and final variables. That means you cannot add any code in your implementation of an interface; all you can do is just provide implementations for all abstract methods and mark all variables with final . So why do we use interfaces? Interfaces are used to enforce information hiding and software modularity. If a class implements multiple interfaces, it must implement every method defined in these interfaces. Thus, if we have multiple abstract classes that contain common functionality, it would be good to factor them out into an interface so that these common functionalities can be shared between these classes by implementing them as abstract methods of an interface.

What is memory leak?

Java has its own garbage collector (GC) to manage memory. Sometimes, however, things go wrong and objects that are no longer used stay in memory. These unused objects are called memory leaks. The most common cause of memory leaks is unintentional object references left behind by developers. A memory leak is just like any other kind of resource leak. It occurs when an application uses more system resources than it releases back to the system for reuse. This can be due to many factors including poor programming practices, bugs or negligence but does not refer to a total depletion of available resources.

What are the differences between abstract class and interface?

It is possible for a class to implement multiple interfaces at once. So if we have an interface and an abstract class with similar functionality, what do we need to do in order to achieve polymorphism? Which one should we use? Well, in general interfaces are preferable over abstract classes as they give a clear definition of behavior without any implementation details. Additionally, it is easier to unit test an interface that it is to unit test an abstract class or concrete class. Abstract classes are generally not intended for use by developers so they don’t provide enough information about their behaviors and how to interact with them. As long as your design doesn’t expose too much functionality then using an interface instead of an abstract class is probably a good idea.

What are valid levels in Inheritance Hierarchy?

A valid level in Inheritance Hierarchy is one that can be inherited by other classes. A Valid level will consist of following items Method overloading is that you can use same method name with different number of parameters. This is different from function overloading, where you have same function name with different parameters. Java code can't have multiple class definitions with same name but different parameter list. So, if we try to do that then compiler will give error like duplicate definition error or compile time error. If methods have identical argument lists, but differ in return type or exceptions thrown, they are said to be overloaded methods in java programming language.

What do you mean by data encapsulation?

All these questions are about data encapsulation and each question is unique. Here’s how to answer them. When you first start learning about object-oriented programming, you learn about things like classes, objects, properties, methods, and events—these are all parts of objects that help you organize your code and make it easy to reuse. Data encapsulation focuses on hiding all of those details behind private access modifiers that keep other classes from messing with your code. A class can store information in its variables or properties that other classes might need access to—like an employee record storing employee ID numbers, names, job titles etc.—and they can use getters/setters so they don’t have to worry about making their code public when they want to update values stored there.

What is method overloading in java?

Method overloading is an essential concept to grasp in order to write better code. While it may seem complicated at first, method overloading is actually quite simple, and you will find many uses for it in your day-to-day programming jobs. So get out of bed, put down that snooze button, and pay attention because we’re going to talk about how you can use method overloading in your next project!

Explain about get() & set() methods.

A set() method is used to assign values to an instance variable. The value is passed in through its parameter. The setter can return any value. If it returns void, we say that it doesn’t return anything (rather than that it returns null). Some programmers choose to explicitly check for null and handle those cases separately, but some find it clearer not to do so. (It’s common practice in Java programs, though.) Similarly, get() methods are used to retrieve values from an instance variable. Their parameter tells them which field of which object they should retrieve.

Differentiate between public, protected, private, package access modifiers.

The dispose() method is called when you are finished with an object. The finalize() method is never called by your program, but rather gets called at some point after your program has exited. The main difference between finalize() and dispose() is that finalize() accepts an argument of type Object, while dispose() accepts no arguments. Finalize(): When should you use it? Dispose(): When should you use it?

How does Garbage Collection work in Java.

Garbage collection, or GC, is one of many memory management techniques used by programming languages. It’s important to understand what happens when your code creates new objects in your program and why GC is essential to application performance. Garbage collection relies on algorithms that determine which parts of memory are being used and which can be safely cleaned out by deleting unreferenced objects and releasing their resources for use elsewhere. If you’re preparing for interviews as an experienced programmer, it’s likely you already know how it works. But if you don’t, here are five interview questions that will help you get up to speed before sitting down with an interviewer. 1) How does garbage collection work in Java? 2) What kind of garbage collectors are there?

Difference between finalize() & dispose() methods?

The Finalize() method is used by an object to release any unmanaged resources it might have, such as file handles or other operating system resources. The Dispose() method performs cleanup operations that must be performed before an object is reclaimed by garbage collection. System resources are automatically released when an object's Finalize() method is called; however, you can't depend on finalization to happen at any particular time.

What are garbage collector strategies in java ?

Garbage collection strategies can be categorized as manual, semi-automatic and automatic. Manual garbage collection is not preferred for large scale applications. The basic idea of manual garbage collection is freeing memory manually by implementing a reference queue (memory manager). However, we need to release references in reverse order so that there are no dangling pointers. Explicit memory allocation and deallocation cause performance overhead due to locking resources that could otherwise be used by other processes while synchronizing among threads. Also they make code prone to error when developers don’t follow well defined rules or use incorrect memory management strategy. To overcome these issues, several garbage collectors with different strategies were developed over years; below are few of them

Explain Heap Space vs Stack Space.

As you’re creating your code, you’ll notice that there are different types of variables. The ones we haven’t covered yet are local and instance. Local variables can only be used in methods, while instance variables can be used in any method within an object. Instance variables exist outside of an object as well and are stored in stack space, while local variables exist inside methods but live in heap space. Heap space is created when an object is instantiated, so it has no limit to how many objects it can hold. Stack space is limited by how much memory is available on a machine at one time; when you run out of memory, things start to crash!

How to check if array contains duplicate elements in java ?

1. If array is of primitive data type then use == operator to check if array contains duplicate elements or not. 2. If array is of reference data type then use equals() method to check if array contains duplicate elements or not. 3. If array is of List data type then use contains() method to check if array contains duplicate elements or not. 4. Check for duplicates in an ArrayList using Arrays class in java . 5. Check for duplicates in an ArrayList using Collections class in java . 6. Check for duplicates in an ArrayList using Arrays class and HashSet class together in java . 7. Check for duplicates in an ArrayList using HashSet class and Collections class together in java . 8.

What happens when you try to compile or run below code segment in Java ?

The code will compile and run without any problem in java, but in python below statement will raise Syntax error. However all valid Python statements are valid in Java. So lets see why it is so ? The main difference between both languages is that while creating variables in Java we need to specify their data type explicitly whereas variables can be created with no data type specified (they are dynamically typed) in Python. This means that if you try to assign a value of string type to an integer variable or vice versa then you will get compilation error as shown above for Python . But you don't need to worry about types when working with Java . It automatically assigns values of appropriate types based on what you're trying to do.