Why is Java called platform independent?
Java is platform independent because you compile your code once into bytecode rather than machine code. That bytecode runs on any device that has a JVM, and each operating system has its own JVM. This is the write once run anywhere idea, since the same compiled file works on Windows, Mac, and Linux.
How it works
When you compile Java you do not get code for a specific processor. You get bytecode, an intermediate form. The JVM on each machine translates that bytecode into instructions the local hardware understands, so your program does not care what machine it runs on.
// Source (.java) -> javac -> Bytecode (.class) -> JVM -> runs anywhereThe bytecode is the same everywhere. What changes is the JVM, which is built for each platform. That is the clever split that gives Java its portability.
Say the phrase write once run anywhere, then explain that bytecode is portable while the JVM is platform specific. Being able to name bytecode as the reason, not just repeat the slogan, is what separates a strong answer.
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