Java Developer Interview Questions and Answers

Java Interview Questions

Java is an object-oriented, cross platform, multi-purpose programming language produced by Sun Microsystems. First released in 1995, it was developed to be a machine independent web technology. It was based on C and C++ syntax to make it easy for programmers from those communities to learn.

JAVA was developed by Sun Microsystems Inc in 1991, later acquired by Oracle Corporation. It was developed by James Gosling and Patrick Naughton. It is a simple programming language.  Writing, compiling and debugging a program is easy in java.  It helps to create modular programs and reusable code.

The original and reference implementation Java compilers, virtual machines, and class libraries were originally released by Sun under proprietary licenses. Sun released the first public implementation as Java 1.0 in 1995. It promised Write Once, Run Anywhere (WORA), providing no-cost run-times on popular platforms.

n 13 November, 2006, Sun released much of Java as free and open source software under the terms of the GNU General Public License (GPL). As of May 2007, in compliance with the specifications of the Java Community Process, Sun relicensed most of its Java technologies under the GNU General Public License. Others have also developed alternative implementations of these Sun technologies, such as the GNU Compiler for Java (bytecode compiler), GNU Class path (standard libraries), and IcedTea-Web.

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Java Virtual Machine (JVM):

Java Virtual Machine (JVM) is a specification that provides runtime environment in which java bytecode can be executed. As the name implies, the JVM acts as a “virtual” machine or processor. Java’s platform independence consists mostly of its Java Virtual Machine (JVM) Java was designed to allow application programs to be built that could be run on any platform without having to be rewritten or recompiled by the programmer for each separate platform.

A Java virtual machine makes this possible because it is aware of the specific instruction lengths and other particularities of the platform. The JVM performs following operation:

  • Loading code
  • Verifies code
  • Executes code


Bytecode (Intermediate code) is object-oriented programming (OOP) code compiled to run on a virtual machine (VM) instead of a central processing unit (CPU). The VM transforms program code into readable machine language for the CPU because platforms utilize different code interpretation techniques. A VM converts bytecode for platform interoperability, but bytecode is not platform-specific. Bytecode is in a compiled Java programming language format and has the .class extension executed by Java Virtual Machine (JVM)

Java Development Kit (JDK):

JDK (Java SE Development Kit) includes a complete JRE (Java Runtime Environment) plus tools for developing, debugging, and monitoring Java applications. JDK is required to develop and run Java applications and applets.

Java Runtime Environment (JRE):

The Java Runtime Environment (JRE), also known as Java Runtime, is part of the Java

Development Kit (JDK), a set of programming tools for developing Java applications. The Java Runtime Environment provides the minimum requirements for executing a Java application; it consists of the Java Virtual Machine (JVM), core classes, and supporting files.

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