Top 25 Java Interview Questions and Answers 2023

Are you aspiring to become a Java developer? You have chosen the right path because Java is one of the widely used programming languages to develop applications and supports billions of devices across the globe. This Java interview questions and answers blog has been designed to provide readers with detailed knowledge on the frequently asked Java interview questions.

In a typical interview the interviewer starts with asking basic Java interview questions, so let's start our learning process with basic Java interview questions and then move to the advanced levels. By mastering these questions you will definitely gain all the confidence to clear your interview. Let's get into the basic java interview questions part.

For better understanding, we have categorized Java interview questions and answers 2023 into 2 parts:

Java Interview Questions and Answers For Freshers

1) What is Java?

Java is a popular Open-source programming language and computing platform released by Microsystems in the year 1995. It is a high-level, robust, object-oriented, high-performance, platform-independent, object-oriented, and portable programming language.

2) Name a few supported platforms by Java?

Java is highly flexible and supports multiple platforms. Java can be run on popular platforms such as OS, Windows, and different versions of UNIX/Linux like Sun Solaris, Ubuntu, Redhat Linux, CentOS, HP-Unix, etc.

3) What are the features of the Java programming language?

Following are the essential Java features which made it a popular programming language.

Object-oriented
Robust
Platform Independent
Multi-threaded
Interpreted,
Architecture Neutral
Distributed
High Performance
Dynamic.

4) How is Java able to give high performance?

Java is able to provide high performance with the help of its Just-in-Time compiler. The Just-In-Time compiler is a run time component that converts the bytecodes to native machine code at run time which improves the performance of Java applications.

5) What is the reason behind calling Java platform-independent?

Java is being called platform-independent because of its byte codes. These byte codes can be executed on any system despite the underlying OS.

6) Why is Java not called as a 100% Object Oriented?

Java is not 100% object-oriented because it uses the 8 primitive data types which are short, long, double, float, int, char, byte, boolean, etc.

7) What do you know about Java Virtual Machine?

Java Virtual Machine (JVM) is a virtual machine that supports a system to run Java programming. JVM is a specification needed to be configured in the computer system. It converts the Java code to a Bytecode which is close to the native code.

8) What do you know about JDK, JRE and JVM?

JDK: JDK is abbreviated as a Java Development Kit and it is a software development environment using which one can develop java applications and applets. It comes with JRE + development tools and exists physically.
JRE: JRE stands for Java Runtime Environment. It consists of a set of software tools that helps in developing Java applications. It provides the runtime environment in Java. It consists of a set of libraries + other files which support JVM during runtime.
JVM: JVM stands for Java Virtual Machine and provides a runtime environment in which Java bytecode gets executed. JVM is platform-independent and available for multiple hardware and software platforms. There are three notions available in JVM which are instance, specification, and implementation.

9) What is meant by platform?

A platform is defined as a software or hardware environment in which software can be run. Java is a Software-based platform.

10) What is Access Modifier in Java?

The Access Modifier option in Java allows you to define the access levels for variables, classes, constructors, and methods. An Individual can have default accessibility or package when there is no Access modifier is defined.

11) What do you know about Packages in Java?

Packages are helpful for grouping the related classes. It is similar to a file in a directory. Packages are helpful for writing better maintainable code and avoiding name conflicts. In Java, we have two types of Packages which are:

Built-in Packages
User-Defined Packages.

12) What are the advantages of Java Packages?

Following are the advantages of implementing Packages in Java:

Packages eliminate the Name clash issues
Provides better access control
We can make use of hidden classes
Easy to spot classes that are related to each other.

13) Why are pointers not implemented in Java?

Java doesn’t use pointers because they increase the complexity of the program and are unsafe. Java is well known for simple code, and mixing it up with pointers will pave roots for the complexity. Pointers are discouraged in Java due to direct access to Memory.

14) How can a Java Class be defined?

A Java class includes all your data and comes with the fields (variables) and methods to control the behaviour of an object. Below mentioned is the syntax of the Class

1
2
3
class Abc {
member variables // class body
methods}

Java Interview Questions and Answers For Experienced

15) What is meant by Object Oriented Programming?

It is popularly known for OOPs and is a programming approach or model where programmes are developed around objects instead of functions and logic. Object-Oriented programming language mainly focuses on the specific objects that need manipulations and not on the logic. This model is well situated for writing complex codes and large programmes and need to be maintained and updated regularly.

16) What is meant by Encapsulation in Java?

Encapsulation is a method used in java to turn the fields into private ones and enable access via public methods. If a field is declared as private then the individuals out of this class are not allowed to access it. It is also called data hiding.

17) What is the main advantage of Encapsulation?

The main advantage of Implementing Encapsulation is that one can make changes to the code without breaking or causing disturbance to others who use this code. Encapsulation improvises code flexibility, maintainability, and extensibility.

18) What is meant by loops concept and how many loops do we have in Java?

Looping is a famous concept in the programming world and used for executing statements repeatedly. In Java, we often use three types of loops which are:

For Loops
While Loops
Do While Loops.

19) What do you know about Java String Pool?

String Pool in Java is defined as a collection of strings and these strings are stored in heap memory. String pool conducts a check whenever a new object is created and examines whether the object is already there in the pool or not. If it is present in the pool then the same is assigned to a variable otherwise a new object will be created.

20) What are the use cases?

Use cases are a part of an analysis program and define a situation that a programme may come across and how the program should act in such types of circumstances.

21) What is the Transient variable in Java?

A transient variable is a variable in Java that may or may not be taken into consideration during the Serialization process. But During the de-serialization process, it will be initialized by its default value.

22) What is meant by Synchronization?

In Java, Synchronization is a technique used to control the accessibility of multiple threads of shared resources. It provides locking data and ensures the access is reliable and eliminates data race.

23) Explain the major difference between the Error and Exception?

Error is a sudden and irrecoverable condition that prevails during the run time. Example: OUtOfMemory. Exceptions are nothing but conditions that arise due to incorrect input, etc. Ex. FileNotFoundException.

24) What do you know about the classloader in Java?

It is a sub-component of the JCM and handles the class file-loading tasks. Each Java program is loaded by the classloader for execution purposes. We have three built-in functions in classloaders:

Extension ClassLoader
Bootstrap ClassLoader
System/Application ClassLoader.

25) What is Inheritance in Java?

Inheritance is a popular concept in Java in which the properties of a class are inherited by the other class. It establishes the relationship between various classes and helps us to reuse the code. Inheritance can be performed between the following classes:

Child class
Parent class.

Conclusion

Cracking a Java Interview is very easy if you have solid preparation. Till now we have come across all the important questions that are asked in any Java Interview. Mastering these Java basic interview questions would help you set yourself apart from the crowd and secure your dream job. Hope this Java Interview questions and answers blog has helped you gain some knowledge. Happy learning!