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Difference Between JDK and JRE in Java

Last Updated : July 24, 2025

To develop or run Java applications, you must understand the roles of the JDK (Java Development Kit) and JRE (Java Runtime Environment). Both are essential components of the Java platform, serving different purposes for developers and users.

What is JDK?

JDK stands for Java Development Kit. It is a full-featured software development kit required to develop Java applications. The JDK includes tools to write, compile, and debug Java programs, as well as everything that is part of the JRE.

JDK = JRE (JVM + Libraries) + Development Tools

Key Components of JDK

Java Compiler: Converts Java source code (.java) into bytecode (.class).
Java Debugger: Helps identify and fix bugs in code.
JVM: Java Virtual Machine to execute bytecode.
Java Libraries: A set of built-in classes and APIs used by Java programs.

JDK Example

Suppose you are a Java developer. You will use the JDK to:

Write Java code (e.g., Sample.java)
Compile the code using javac to get Sample.class
Execute the code using java command to see the output

public class Sample {
    public static void main(String[] args) {
        System.out.println("Welcome Java");
    }
}

When you run the above code, the output will be:

Welcome Java

What is JRE?

JRE stands for Java Runtime Environment. It is a subset of the JDK used only to run Java applications. JRE does not include development tools such as the compiler or debugger, but it does include the JVM and standard Java class libraries.

JRE = JVM + Libraries

Key Points about JRE

Provides the minimum environment to run Java programs.
Used by end-users or clients who want to execute Java applications.
Does not support writing or compiling Java code.
JRE is a part of JDK, but JDK is not a part of JRE.

JRE Example

Suppose you are a user of a Java application. You just need JRE to:

Run the compiled Java bytecode (e.g., Sample.class)

java Sample

This will output:

Welcome Java