Java has three main components: the Java Virtual Machine (JVM), the Java Runtime Environment (JRE), and the Java Development Kit (JDK).

1. JVM (Java Virtual Machine) - The JVM is the runtime engine that executes Java bytecode. It provides a platform-independent environment for Java programs to run on any system that has a JVM installed. The JVM is responsible for interpreting Java bytecode and translating it into machine code that can be executed by the underlying operating system. This allows Java programs to run on any platform, regardless of the hardware or operating system.

2. JRE (Java Runtime Environment) - The JRE is a subset of the JDK that includes the JVM, as well as other essential components needed to run Java applications. It provides a runtime environment for Java programs to execute, without including the development tools such as the Java compiler and other utilities. JRE includes the class libraries that are required for the execution of Java programs.

3. JDK (Java Development Kit) - The JDK is a full-featured software development kit that includes everything you need to develop, compile, and run Java applications. It includes the JRE, the Java compiler, and other development tools such as the debugger, documentation generator, and more. The JDK is used by developers to write and test Java programs.