Java Compiler and Java Virtual Machine

 

⚙️ Java Compiler and Java Virtual Machine (JVM)

Java uses a two-step process to run programs:

Step 1: Java Compiler (javac)

The Java compiler is a program that:

• Converts Java source code (.java file) into bytecode (.class file).

• Bytecode is an intermediate, platform-independent code.

📌 Example:
When you write:

public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello, World!");
    }
}

Save it as HelloWorld.java.

Now compile it:

javac HelloWorld.java

This creates a file called HelloWorld.class — which contains bytecode.

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Step 2: Java Virtual Machine (JVM)

The JVM is a virtual engine that:

• Reads and executes the bytecode (.class file).

• Converts bytecode to machine-specific code using Just-In-Time (JIT) compilation.

• Ensures that the same .class file can run on any device with a JVM (Windows, Mac, Linux, etc.).

📌 To run the program:

java HelloWorld

The JVM runs the bytecode and produces the output:

Hello, World!

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🎯 Why is this important?

Component	Role	Output
javac	Java Compiler	.class bytecode file
java (JVM)	Executes the bytecode on your machine	Program output on console

Summary

• Java Compiler (javac) ➜ Converts .java to .class (bytecode).

• JVM (java) ➜ Runs the bytecode, making Java platform-independent.