java - Why is android.app.Activity not abstract by design? -

why android.app.activity not abstract design if documentation/tutorials @ least method oncreate() must implemented.

from http://developer.android.com/guide/components/activities.html

you must implement method. system calls when creating activity.

even if not mentioned explicitly, without implementation there no point in having android.app.activity object, or? understand parrent needs execute code in own implementation of oncreate() surely there can design when part of parent oncreate() a call abstract call-back method needs implemented developer.

example of design:

public abstract class activity {       public abstract void implementthis(object o);      public void oncreate(object o){         //do stuff         implementthis(o);         //do other stuff or end.     }  } 

am missing here? why there non-abstract activity if developer must , needs subclass , provide custom implementation?

read here: http://grepcode.com/file/repository.grepcode.com/java/ext/com.google.android/android/1.5_r4/android/app/activity.java#activity.oncreate%28android.os.bundle%29

"the default implementation of method performs restore of view state had been frozen onsaveinstancestate(android.os.bundle)."