If this question comes up, then it probably means you're doing something wrong. In good object-oriented design, it generally doesn't make sense to call a method outside of the context of a particular object. In other words, you shouldn't be wanting to just call a function;
you should have an object and want to invoke a method on it for some reason.
If you understand what I'm saying, the next question is, What to do about it? Consider these three possibilities (and probably more
1) The method you want to call doesn't belong in that other class; it actually belongs in
this class, where the method is convenient;
2) The code you're writing doesn't belong in
this class, but rather in that
other class, where it can call the method on itself.
3) In some cases, the method really doesn't need to be attached to an object; in that case it should be static. But too many static methods indicates, again, a non-object-oriented design; it's a problem that many new to
Java have.