How Java is Platform Independent?

Java is known for being platform independent, and this is possible due to the use of bytecode and the Java Virtual Machine (JVM).

First, a Java program is written and saved with a .java extension. This source code is compiled using the javac command, which produces bytecode (a .class file). Bytecode is an intermediate code that is not specific to any operating system.

This bytecode is then executed using the java command, which hands it over to the Java Virtual Machine (JVM). The JVM is available for various platforms such as Windows, Linux, and macOS.

Inside the JVM, the Java Interpreter plays a key role. It reads the bytecode line by line and translates it into machine-specific instructions that the operating system can understand. In some modern JVMs, a Just-In-Time (JIT) compiler is also used to improve performance by converting bytecode into native code more efficiently.

Because each platform has its own JVM, and the JVM interprets the same bytecode accordingly, the same Java program can run on multiple systems without any changes.

This process supports Java's WORA model (Write Once, Run Anywhere).

Example shown in diagram:

If a Java program is written and compiled on a Windows system, the .class file (bytecode) can be uploaded to the internet and later downloaded on a macOS or Linux machine. The JVM on each system uses the Java Interpreter to execute the program correctly, without requiring any modifications.

Java: A Compiled and Interpreted Language

Java is a compiled and interpreted language, which means that it goes through both compilation and interpretation during its execution. Here's how it works:

1. Compilation: Java source code (written in .java files) is first compiled using the javac command. This produces bytecode (.class files). Bytecode is a platform-independent code, which means it can run on any system with a Java Virtual Machine (JVM).
2. Interpretation: After the code is compiled into bytecode, it is passed to the Java Virtual Machine (JVM). The JVM then interprets the bytecode into machine-specific code, which the computer’s operating system can execute. This happens at runtime, making Java a partially interpreted language.

In this way, Java achieves its platform independence—you write the code once and it can run anywhere, thanks to the combination of compilation and interpretation.