In this post, we will learn the difference between JDK and JRE, and JVM in Java. This is a frequently asked question in Java interviews for beginners. Let's dive into it.
Overview
JVM (Java Virtual Machine): JVM is an abstract machine that provides a runtime environment in which Java bytecode can be executed. It's platform-independent, which means you can run the same Java program on different operating systems.
JRE (Java Runtime Environment): The JRE is an implementation of the JVM which actually executes Java programs. It includes the JVM, core libraries, and other additional components to run applications and applets written in Java.
JDK (Java Development Kit): The JDK is a software development environment used for developing Java applications and applets. It includes the JRE, an interpreter/loader (java), a compiler (javac), an archiver (jar), a documentation generator (Javadoc), and other tools needed in Java development.
| JDK | JRE | JVM |
|---|---|---|
| JDK stands for Java Development Kit. It is a software development environment used to develop Java applications and applets. It includes the JRE, an interpreter/loader (java), a compiler (javac), an archiver (jar), a documentation generator (Javadoc), and other tools needed in Java development. | JRE stands for Java Runtime Environment. It provides the minimum requirements for executing a Java application. It includes the JVM, core classes, and supporting libraries. | JVM stands for Java Virtual Machine. It is an abstract machine that provides a runtime environment in which Java bytecode can be executed. |
| The JDK allows developers to create Java programs that can be executed and run by the JVM and JRE. | JRE is essentially a software package that contains what is required to run a Java program. It is the implementation of JVM. | JVM is responsible for executing the Java program line by line hence it is also known as an interpreter. It also provides functionalities like memory management, garbage collection, security, etc. |
| Developers need JDK installed on their system in order to develop Java programs and applications. | End-users need JRE installed on their system to run Java programs. | JVM is a part of both JDK and JRE that interprets the bytecode into the machine code and executes it. |
| Example: OpenJDK | Example: Oracle's JRE | Examples: HotSpot, J9, etc. |
| JDK includes development tools for developing, debugging, and monitoring Java code. | JRE does not contain any development tools like Java compiler, debugger, etc. If you only want to run Java programs on your browser or computer you would only need JRE. | JVM interprets the byte code into the machine code depending upon the underlying operating system and hardware. |
Understanding the Relationship
The relationship between JVM, JRE, and JDK is important to understand. The JDK is for development purposes, which is why it includes development tools such as the Java compiler. The JRE provides the environment to run the Java program and is a part of the JDK. The JVM is what makes the whole process platform-independent, executing the Java program line by line.
In essence, when you write and run a Java program, you're using the JDK to compile Java code into bytecode. This bytecode is executed by the JVM, which is provided by the JRE.
Conclusion
JDK, JRE, and JVM are three core components of Java programming. They work together to compile, run, and execute Java programs. While JDK is used for developing applications, JRE is for running them, and JVM ensures that the whole process is platform-independent. Having a clear understanding of these three components and their relationships will help you navigate the world of Java programming more effectively.
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