Question

I would like to make abstract class which has several inner classes extend it and could create instances of its inner classes via static methods but I get compiler error “No enclosing instance of type ITask is accessible. Must qualify the allocation with an enclosing instance of type ITask (e.g. x.new A() where x is an instance of ITask).”

I’ve found out that inner classes should be created by instances of outer class but my outer class has abstract method and I can’t create instance of it. I made inner classes which extend parent because I wont to control creation of them.
So is there any way how to make my pattern works.

My code:

public abstract class ITask {
public abstract void Execute(Subscriber itm);

static public ITask CreateSendTask(Buffer buffer)
{
    return new SendData(buffer);
}

static public ITask CreateSTTask(Ticket sid)
{
    return new StartTransmission(sid);
}

static public ITask CreateETTask(Ticket sid)
{
    return new EndTransmission(sid);
}


private class SendData extends ITask
{
         /// some implemetation...
}

private class StartTransmission extends ITask
{
         /// some implemetation...
}

private class EndTransmission extends ITask
{
    /// some implemetation...
}

}

The problem is with methods Create(.*)Task.

Thanks!

Answer 1

The inner classes should be made static if they’re created from static methods, and thus don’t need access to an enclosing ITask.

You should also respect Java naming conventions: methods start with a lower-case letter.