JDK vs JRE vs JVM in Java: Key Differences and Usage

In Java, JVM (Java Virtual Machine) runs Java bytecode on any device, JRE (Java Runtime Environment) provides the libraries and JVM to run Java programs, and JDK (Java Development Kit) includes JRE plus tools to develop Java applications.

Quick Comparison

Here is a quick table comparing JDK, JRE, and JVM based on their main features and roles.

Aspect	JVM	JRE	JDK
Full Name	Java Virtual Machine	Java Runtime Environment	Java Development Kit
Purpose	Runs Java bytecode	Runs Java programs	Develops and runs Java programs
Includes	Only JVM	JVM + libraries + other files	JRE + development tools (compiler, debugger)
Usage	Execution of Java bytecode	Execution environment for Java apps	Development and execution
Contains Compiler	No	No	Yes (javac)
Target Users	End users and JVM implementers	Users running Java apps	Java developers

Key Differences

The JVM is the core part that actually runs Java bytecode on your machine. It acts like a translator between the compiled Java program and your computer's hardware, making Java platform-independent.

The JRE includes the JVM plus standard libraries and other files needed to run Java applications. It does not include tools to write or compile Java code, so it is meant for users who only want to run Java programs.

The JDK is a full package for Java developers. It contains the JRE and also tools like the Java compiler (javac), debugger, and other utilities needed to create Java applications. Without the JDK, you cannot write or compile Java code.

Code Comparison

Here is a simple Java program that prints "Hello, Java!". This code is compiled and run using the JDK and executed by the JVM inside the JRE.

java

public class HelloJava {
    public static void main(String[] args) {
        System.out.println("Hello, Java!");
    }
}

Output

Hello, Java!

JRE Equivalent

The JRE does not compile Java code but runs the compiled bytecode. Here is how you run the compiled program using the java command from the JRE.

shell

java HelloJava

Output

Hello, Java!

When to Use Which

Choose JVM when you want to understand or implement how Java bytecode runs on different platforms. Choose JRE if you only need to run Java applications without developing them. Choose JDK if you want to write, compile, and debug Java programs because it includes all necessary tools for development.

Key Takeaways

JVM runs Java bytecode and makes Java platform-independent.

JRE includes JVM and libraries to run Java programs but lacks development tools.

JDK includes JRE plus tools like the compiler to develop Java applications.

Use JRE for running Java apps and JDK for developing them.

JVM is the core engine inside both JRE and JDK.