Top Java Interview Questions to Help You Prepare For Job Interview

Java has turned out to be one of the main tools in the software development domain.  Professionals keen on doing well in the software industry are expected to learn and master Java skills. In this article, we have curated some the most asked Java Interview Questions that will help you crack interview processes and showcase your knowledge at any test. 

1. What is thread in java?

Ans: A thread in Java refers to a process that allows a program to operate more efficiently by doing multiple things at the same time. Threads can be used to perform complicated tasks in the background without interrupting the main program.

It can be created by extending the Thread class and overriding its run() method:

Extend Syntax

public class MyClass extends Thread {

public void run() {

System.out.println(“This code is running in a thread”);

}

}

2. How to take input in java?

Ans: “Scanner in = new Scanner(System.in);

      System.out.print(“”Please enter hour 1: “”);

      int hour1 = in.nextInt();

      System.out.print(“”Please enter hour 2: “”);

      int hour2 = in.nextInt();

      System.out.print(“”Please enter minute 1: “”);

      int min1 = in.nextInt();

      System.out.print(“”Please enter minute 2: “”);

      int min2 = in.nextInt();”

3. How to install java?

Ans: Java can be installed through a command prompt so that it can generate necessary log files to troubleshoot the issue.

->Go to java.com and click on the Free Java Download button.

->Click on the Save button and save Java software on the Desktop

->Verify that Java software is saved on the desktop.

->Open Windows Command Prompt window.

->Windows XP: Click Start -> Run -> Type: cmd

Windows Vista and Windows 7: Click Start -> Type: cmd in the Start Search field.

cd <Java download directory> (for example Downloads or Desktop etc.).
IRun the installer and follow onscreen instructions.

4. How to reverse a string in java?

Ans: “String str = “”Hello””;

String reverse(String str){

  StringBuilder sb = new StringBuilder();

  sb.append(str);

  sb.reverse();

  return sb.toString();

}”

5. How to set path in java?

Windows 10 and Windows 8

In Search, search for and then select: System (Control Panel)

Click the Advanced system settings link.

Click Environment Variables. In the section System Variables, find the PATH environment variable and select it. Click Edit. If the PATH environment variable does not exist, click New.

In the Edit System Variable (or New System Variable) window, specify the value of the PATH environment variable. Click OK. Close all remaining windows by clicking OK.

Reopen Command prompt window, and run your java code.

Mac OS X

To run a different version of Java, either specify the full path or use the java_home tool:

% /usr/libexec/java_home -v 1.8.0_73 –exec javac -version

Solaris and Linux

To find out if the path is properly set:

In a terminal windows, enter:

% java -version

This will print the version of the java tool, if it can find it. If the version is old or you get the error java: Command not found, then the path is not properly set.

Determine which java executable the first one is found in your PATH

In a terminal window, enter:

% which java

6. What is enumeration in java?

Ans: In Java, enumeration defines a class type. Enumeration refers to a list of named constant. An Enumeration can have constructors, methods and instance variables. It is created using enum keyword. Each enumeration constant is public, static and final by default. An enumeration defines a class type and has constructors. Enumeration variables are used and declared in much the same way as you do a primitive variable.

7. What is inheritance in java?

Ans: Inheritance in Java refers to the process by which one class acquires the properties (data members) and functionalities(methods) of another class. The aim of inheritance is to provide the reusability of code so that a class has to write only the unique features and rest of the common properties and functionalities can be extended from another class.

Child Class:

The class that extends the features of another class is known as child class, sub class or derived class.

Parent Class:

The class whose properties and functionalities are used(inherited) by another class is known as parent class, super class or Base class.

8.How to compare two strings in java?

Ans: “// These two have the same value

new String(“”test””).equals(“”test””) // –> true 

// … but they are not the same object

new String(“”test””) == “”test”” // –> false 

// … neither are these

new String(“”test””) == new String(“”test””) // –> false 

// … but these are because literals are interned by 

// the compiler and thus refer to the same object

“”test”” == “”test”” // –> true “

9. What is abstraction in java?

Ans: Abstraction in Java refers to the general procedure of accessing functions and properties of any program. Objects are the building blocks of Object-Oriented Programming. An object contains some properties and methods. We can hide them from the outer world through access modifiers. We can provide access only for required functions and properties to the other programs.

10. What is encapsulation in java?

Ans: Encapsulation refers to the process of hiding implementation details from users. If a data member is private it means it can only be accessed within the same class. No outside class can access private data member (variable) of other class.

However if we setup public getter and setter methods to update (for example void setName(String Name ))and read (for example String getName()) the private data fields then the outside class can access those private data fields via public methods.

11. What is a collection in java?

Ans: A Collections is like containers that group multiple items in a single unit. For example, a jar of chocolates, list of names, etc.

Collections are used in every programming language and when Java arrived, it also came with few Collection classes – Vector, Stack, Hashtable, Array.

12. What is api in java?

Ans: Java application programming interface (API) is a list of all classes that are part of the Java development kit (JDK). It includes all Java packages, classes, and interfaces, along with their methods, fields, and constructors. These pre-written classes provide a tremendous amount of functionality to a programmer.

13. How to initialize array in java?

Ans: “int[] arr = new int[5]; // integer array of size 5 you can also change data type

String[] cars = {“”Volvo””, “”BMW””, “”Ford””, “”Mazda””};”

15. How to take input from user in java?

“import java.util.Scanner;

  Scanner console = new Scanner(System.in);

  int num = console.nextInt();

  console.nextLine() // to take in the enter after the nextInt() 

  String str = console.nextLine();”

16. What is static in java?

In Java, a static member is a member of a class that isn’t associated with an instance of a class. Instead, the member belongs to the class itself. As a result, you can access the static member without first creating a class instance.

17. What is package in java?

A package in Java is used to group related classes. Think of it as a folder in a file directory. We use packages to avoid name conflicts, and to write a better maintainable code. Packages are divided into two categories:

Built-in Packages (packages from the Java API)

User-defined Packages (create your own packages)

18. What is an abstract class in java?

A class that is declared using the “abstract” keyword is known as abstract class. It can have abstract methods (methods without body) as well as concrete methods (regular methods with body). A normal class (non-abstract class) cannot have abstract methods.

19. How to enable java in chrome?

Ans: To enable java in chrome, follow these steps:

->In the Java Control Panel, click the Security tab

->Select the option Enable Java content in the browser

->Click Apply and then OK to confirm the changes

Restart the browser to enable the changes

Hope these questions help you prepare for your dream role in the industry. Let us know if you have any additional questions. Keep learning and all the best!