What is the meaning of "Java is portable"?

Question

I'm confused about Java portability. If the Java language is portable, why is enum unknown in J2ME?

In C++, it's not important which platform or library is used. The "C++ language" doesn't change in all platforms.

My purpose is developing a Java library that just uses primitive types like int, String, or Array (something like a library for Genetic algorithms). I want to use this library in mobile and desktop applications. But it seems that enum and some other keywords do not exist in all platforms.

So I think I misunderstood the meaning of "Java portability". What does that mean?

Answer 1

There are three flavors of Java: ME for mobile, SE for desktops, and EE for enterprise.

"Java is portable" refers to the SE version. It means that you can run Java bytecode on any hardware that has a compliant JVM.

It doesn't mean that ME is the same as SE is the same as EE. EE has EJBs, but SE and ME don't. That does not make them less portable.

C++ language doesn't change in all platforms.

This statement is not strictly correct. Microsoft adds extensions to their C++ that won't run elsewhere.

ANSI C++ might mean portable source code, as long as you stay away from platform-specific extensions. It does not mean portable bytecode; you may have to recompile and relink.

You want to run genetic algorithms on phones? I know that mobile devices have become pretty powerful, but I'm educated to think that GA would be a server-side functionality. Mobile devices feel more like view to me.