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Understanding JDK, JRE, and JVM

Key Distinction to remember:​

Platform Independence vs. Platform Dependence:​

  • Java (the language) is platform-independent (Write Once, Run Anywhere).
  • The JVM is platform-dependent. You download a specific JVM for Windows, macOS, or Linux so it can translate that universal bytecode into the specific machine code that the OS understands.

Java Development Kit (JDK)​

  • The Java Development Kit (JDK) bundles the Java compiler (javac), standard libraries, debugger and other tools needed to develop, build and package Java applications.
  • A JDK typically contains a runtime implementation, so it includes the components required to run Java programs. However, a JDK is not strictly required on machines that only need to execute Java, only a runtime is necessary.
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Since Java 11, standalone Java Runtime Environment (JRE) installers are no longer provided, making the JDK the primary distribution for both development and production environments.

Java Runtime Environment (JRE)​

  • JRE is required to run Java applications.
  • It includes a JVM implementation, core libraries, and other components to execute Java bytecode on the host machine.
  • It is intended for runtime only, does not include development tools (compiler, debugger).
  • It supports JVM-based languages but is specific to the Java platform.

Java Virtual Machine (JVM)​

  • JVM runs any program that's compiled to byte code.
  • It acts like an abstract "virtual" computer.
  • It has byte code loader, verifier and interpreter.
  • It can convert byte code to machine specific code at runtime using Just-In-Time (JIT) compiler.