android - Activity Listener Implementation? -

i android/java novice , have question based on following scenario:

1. i have baseactivity extended number of other activities, a1, a2, , a3
2. activities a1, , a2 may request user enter part#s. activity a3 doesn't have functionality never ask part#.
3. part# entered user in partdialogfragment. since user may prompted part# a1 , a2 activities, thinking put code instantiates , shows partdialogfragment in baseactivity don't have duplicate same call in activities a1 , a2.
4. partdialogfragment has interface defines onpartentered()

question: should implement interface partdialogfragment in baseactivity or in activities a1 , a2?

basically, thinking this:

class partdialogfragment extends dialogfragment{     private partlistener mpartlistener;      public interface partnumberlistener{         void onpartentered(string part#);     }     ...     ...    @override   public void onattach(activity activity){     super.onattach(activity);     try{       mpartlistener = (partlistener) activity;     } catch(classcastexception e){       throw new classcastexception(activity.tostring() + " must implement partlistener");     }   }   ...   ... }  public abstract class baseactivity    implements partdialogfragment.partnumberlistener {  //**should implement here?**      ...     ...      public void showpartnumberdialog(){         //creates , shows partdialogfragment defined above     } }  public class a1 extends activity   implements partdialogfragment.partnumberlistener {  //**or in a1 , a2?**     ...     ...     if (something){         showpartnumberdialog();  //this defined in baseactivity     } }  public class a1 extends activity   implements partdialogfragment.partnumberlistener {  //**or in a1 , a2?**     ...     ...     if (something){         showpartnumberdialog();  //this defined in baseactivity     } }  public class a3 extends activity{     ...     ...     //**this never ask part#, no need implement partdialogfragment.partnumberlistener here.** } 

a1 , a2 activities need implement interface, because if base class abstract, definition required create subclasses of instantiate. subclasses required (by compiler) implement interface methods abstract class left out.