Top 10 Java Interview Questions with Answers

Java is a versatile programming language that is based on C++. It is a general-purpose, object-oriented, class-based, concurrent, and the runtime environment independent of platform. It is one of the popular and most used language that is used in different domains such as banking, retail, information technology, Android, financial services, stock market, Big Data, and scientific and research community. This article on Java interview questions covers basic as well as advanced questions on Java programming.

1. What is Java?

Java is a platform-independent high-level programming language developed by Sun Microsystems. It is used for developing a wide variety of applications. It consists of advanced and simplified features and is free to access. It can execute multiple functions at the same time and is developed on the logic of "Write once, Run anywhere."

2. What are the features of Java?

Java is a highly effective programming language that has created an ocean of opportunities. Some of the most brilliant features of it are:

Simplicity: Java is more preferred than other programming language, including C++ because it removed all the complexities like pointers, and operator overloading.

Portable: Being platform-independent, Java has made easy to port any application from one platform to another.

Object-oriented: Java considers everything as an object where it stores different properties, behavior, and features of different categories. These objects are used to perform entire operations.

Secured: Java compiles and converts all the code into bytecode, which is understood only computers that run it. By removing explicit pointer and running programs inside the sandbox, Java has made tampering with applications from untrusted sources impossible. With Java, developers can develop applications free of virus and robust systems/applications.

Dynamic: Java has enabled the reduction of memory wastage and enhancing the performance of the application with its ability to adapt to an evolving environment and support dynamic memory allocation.

Multithreaded: Java makes programming with threads easier by supporting lightweight processes or multiple threads execution.

3. What are the features in Java?

The features of Java are:

Oops concepts:

4. How Java enhances the performance of applications?

Java enhances the performance of applications by using Just in Time compiler, which converts the instructions into bytecodes.

5. What is a Class?

A class is use to refer to variables and methods which is used to define all Java codes. Variables are the features that define the state of a class. Methods are used to perform business logic. It is where the a set of statements or instructions are stored to execute a particular function.

6. Define JDK, JRE, and JVM?

JDK: It is an abbreviation for Java Development Kit used for compiling, documenting, and packaging Java programs. It includes JRE and development tools.

JRE: Java Runtime Environment or JRE is a runtime environment for Java bytecode execution. It is for making JVM active and effective.

JVM: It is Java Virtual Machine, which is an abstract machine. It sends instructions to the computer's processor to execute for the execution of Java bytecode.

7. What makes Java platform-independent?

Because of its features to run bytecodes on any system, regardless of which platform they are written on.

8. Is Java 100% object-oriented. If not, than why?

No. Java is not 100% object-oriented since it used eight primitive data types. Which are: boolean char, byte, float, int. double, short, and long. And all these are not objects.

9. What are Constructors in Java?

They are a block of codes meant for initializing an object. However, their name should be identical to that of the class. Moreover, when an object is created, it automatically gets called because of not having any return type.

10. What are the types of Constructors?

The constructors are of two types:

1.Default Constructor: This constructor is so named because it is created by default, which means without any inputs from the user. It is also called no argument constructor since it doesn't take any inputs. It takes the default values of the instance variables and is used for creating an object.

2.Parameterized Constructor: It is the constructor that has the quality to initialize the instance variables as per the provided values. It is so called because it takes the arguments.

Java is vast which is why there is no way to guess how many questions would be asked in the interview. It totally depends on the interviewer and the time he or she has to interview you.

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