What gives java "Write once and run anywhere" nature?

Answer 1

The Java Virtual Machine. It is available for almost all operating systems, architectures etc. It executes Java byte code. That's why you can't run Java apps unless you download Java.

Answer 2

Java is executing it's code on the JVM (Java Virtual Machine)
Which means that Java's source code doesn't have to adapt to the OS, but the Virtual Machine that runs Java on it has to change.

So instead of Reprogramming Java's Development Kit (JDK), they only have to adapt the JVM to the OS.

Thus you can execute Java programs anywhere on any machine as long as it has JVM installed on it.

Answer 3

Thanks for valuable answer