Java Programming

JDK, JRE and JVM Explained Simply for Java Beginners

By EG Digital Skills Training · Updated 18 October 2026

Almost every Java beginner meets three confusing terms in the first week: JVM, JRE and JDK. They are easy once you see how they fit together.

JVM: the engine that runs Java

The Java Virtual Machine runs compiled Java programs. Because there is a JVM for each operating system, the same compiled program can run on Windows, Linux or macOS. This is the idea behind "write once, run anywhere".

JRE: the runtime

The Java Runtime Environment is the JVM plus the core libraries a program needs in order to run. If you only want to run Java programs, a runtime is enough.

JDK: the developer kit

The Java Development Kit includes the runtime and the tools you need to write programs, such as the javac compiler, the jar tool and a documentation generator. Developers install the JDK.

How a Java program runs

1. You write source code in a .java file.
2. The javac compiler turns it into bytecode in a .class file.
3. The JVM loads the bytecode and runs it on your computer.

javac Hello.java
java Hello

What should you install?

As a learner, install a JDK. Many modern Java distributions are installed as a JDK, so you usually do not download a separate runtime. Check the documentation for the version you use.

A common beginner error

If the terminal says javac is not recognised, the JDK's bin folder is usually missing from your PATH. Set the PATH, and the JAVA_HOME variable if needed, then open a new terminal window.