How to force derived class to call super method? (Like Android does)

Question

I was wondering, when creating new Activity classes and then overriding the onCreate() method, in eclipse I always get auto added: super.onCr

Answer 1

To answer your actual question, the auto-creation of the call to super.onCreate() is a feature of the ADT plugin. In java, you cannot directly force a subclass to call the super implementation of a method, afaik (see the pattern described in other answers for work-around). However, keep in mind that in Android, you are not instantiating Activity objects (or Service objects) directly - you pass an Intent to the system and the system instantiates the object and calls onCreate() upon it (along with other lifecycle methods). So the system has a direct object reference to the Activity instance and is able to check (presumably) some Boolean that is set to true in the superclass implementation of onCreate(). Although I don't know exactly how it is implemented, it probably looks something like this:

class Activity
{
  onCreate()
  {
    superCalled = true;
    ...
  }
  ...
}

And in the "system" level class that receives the Intent and instantiates the Activity object from it:

...
SomeActivitySubclass someActivitySubclassObject = new SomeActivitySubclass();
someActivitySubclassObject.onCreate();
if (!someActivityObject.isSuperCalled())
{
  Exception e = new Exception(...) //create an exception with appropriate details
  throw e;
}

My guess is it's probably slightly more complex than that, but you get the idea. Eclipse automatically creates the call because the ADT plugin tells it to, as a convenience. Happy coding!