java从另一个调用类中的一个函数

Question

class A:

public class A extends Activity{
    B b;

    @Override
    public void onCreate(Bundle savedInstanceState) {
       b.sample();
    }

    public void test(){
       //Do Something
    }
}

Class B:

public class B{

    public void sample(){
       //Do Something
    }
}

Its Ok To call methods Of Class B in the Class A, But How Is it Possible to Call Class A methods And Functions In Class B?

I cant create An New Object Of Class A in Class B like:

A a = new A();

because It then Creates A Whole New Activity (Am I Right?!)

Should I Use Interface to Achieve this?

Answer 1

define the B constructor and make it receive the activity

public class B{
   private Activity theActivityA;
   B(Activity activitiy){
    this.theActivityA = activitiy;
   if(this.theActivityA!=null){
      this.theActivityA.test();
   }
}

Answer 2

Yes, you can use interfaces. I assume that you need to notify the activity about something.

public class A extends Activity implements B.IListener {
....

public class B{
    IListener mListener;
    B(IListener listener){
        mListener=listener;
    }
    public void sample(){
       //Do Something
    }
    public interface IListener {
       something();
    }
}

So, in B you can call methods to any instance of IListener, not just A.

Hope it helps.