How can I create a new class instance from a class within a (static) class?

Question

I'm new to Java (have experience with C#),

this is what I want to do:

public final class MyClass
{
    public class MyRelatedClass
    {
      ...
    }
}

public class OtherRandomClass
{
    public void DoStuff()
    {
       MyRelatedClass data = new MyClass.MyRelatedClass(); 
    }
}

which gives this error in Eclipse:

No enclosing instance of type BitmapEffects is accessible. Must qualify the allocation with an enclosing instance of type BitmapEffects (e.g. x.new A() where x is an instance of BitmapEffects).

This is possible in C# with static classes, how should it be done here?

Answer 1

The way you've defined MyRelatedClass, you need to have an instance of MyClass to be able to access/instantiate this class.

Typically in Java you use this pattern when an instance of MyRelatedClass needs to access some fields of a MyClass instance (hence the references to an "enclosing instance" in the compiler warning).

Something like this should compile:

public void doStuff() {
   MyClass mc = new MyClass();
   MyRelatedClass data = mc.new MyRelatedClass(); 
}

However, if a MyRelatedClass instance does not need access to fields of it's enclosing instance (MyClass's fields) then you should consider defining MyRelatedClass as a static class, this will allow the original code you've posted to compile.

The difference in having a nested class (what you've posted) and a static nested class (a static class within a class) is that in the former, the nested class belongs to an instance of the parent class, while the latter has no such relationship - only a logical/namespace relationship.