Is there a difference between Java platforms?

The language is the same, what changes is its surroundings, the extra libraries (the basic ones are the same). Now, when you talk on mobile, maybe you're talking about Android, you have to be careful because in this platform the implementation is usually delayed and not have everything available in the newer versions of the language, you have to check what you already have can use. Now, if the language changes out of the standard, it can not use the Java name.