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JVM / JRE / JDK

These three terms describe different layers of the Java platform:

JVM (Java Virtual Machine)​

The JVM is the runtime engine that executes Java bytecode.

  • Loads classes, verifies bytecode for safety, and runs code
  • Provides Garbage Collection (GC) for automatic memory management
  • Uses JIT compilation to convert hot bytecode into optimized native machine code

JRE (Java Runtime Environment)​

The JRE is what you need to run a Java program.

  • Includes the JVM + core Java libraries
  • Does not include development tools like the compiler

JDK (Java Development Kit)​

The JDK is what you need to build Java applications.

  • Includes the JRE + developer tools
  • Common tools:
    • javac (compiler)
    • java (launcher)
    • javadoc (documentation generator)
    • jshell (interactive shell)

Simple rule:

  • If you only want to run apps → JRE (practically today, most people just install a JDK)
  • If you want to develop apps → JDK