The Java Runtime Environment (JRE) is a software package that provides the necessary libraries, Java Virtual Machine (JVM), and other components required to run Java applications. It does not include development tools like compilers and debuggers (which are part of the JDK).
- Primary Function: Enables Java applications to execute on any system with the JRE installed.
- Key Components: JVM, core libraries, and supporting files.
- Platform Independence: Java applications run on different OS platforms without modification, thanks to the “Write Once, Run Anywhere” principle.
Key Components
- Java Virtual Machine (JVM): Executes Java bytecode and provides memory management, garbage collection, and runtime optimizations.
- Java Class Libraries: Essential precompiled Java classes (e.g.,
java.lang,java.util,java.io). - Java Class Loader: Loads Java classes into memory dynamically.
- Runtime Libraries & Native Code: System-dependent code required for execution.
How Java Code Runs
- Java source code (
.java) is compiled → Converted into bytecode (.class) by the JDK. - JRE loads and runs the bytecode → Uses JVM, libraries, and runtime components.
- JVM executes the code → Converts bytecode into machine-specific instructions.
- Application runs on any OS → As long as the appropriate JRE is installed.