class Activity implements IListener{

    private Button mButton;

    public void onCreate(){
        mButton=new Button();
        mButton.setOnClickListener(this);
        mButton.doClick();
    }

    @Override
    public void onClick() {
        StdOut.println("onClick");
    }
}

interface IListener{
    public void onClick();
}

class Button{

    IListener mListener;

    public void setOnClickListener(IListener listener){
        mListener=listener;
    }

    public void doClick(){
        mListener.onClick();
    }

}