Code written in Java runs on any operating system without requiring modification. Why? How?

Java code can run on any operating system without needing changes because of a key component called the Java Virtual Machine (JVM).

Think of the JVM as a translator or a middle layer. Here's how it works:

1. When you write Java code, it’s compiled into an intermediate form called bytecode, not directly into machine code for a specific OS.

2. This bytecode is platform-independent—meaning it's the same no matter where it's run.

3. The JVM on each device reads the bytecode and translates it into machine code that the specific operating system and hardware can understand.

Since each OS (Windows, macOS, Linux, etc.) has its own version of the JVM, your Java program doesn't need to change. The JVM handles all the OS-specific translation for you.

Example:

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

Once compiled, this code becomes bytecode in a .class file. That same file can be run on any system that has a JVM installed—no changes required.

This is what people mean when they say "Write once, run anywhere", which is one of Java’s biggest strengths.