View btn1 = this.findViewById(R.id.button1);
btn1.setOnClickListener(new ButtonClickListener());

private class ButtonClickListener implements View.OnClickListener{

       public void onClick(View v) {
             if(R.id.button1 == v.getId())
             {
                   MediaPlayer mediaPlayer01;
                   mediaPlayer01 = MediaPlayer.create(getBaseContext(), R.raw.ring);
                   mediaPlayer01.start();
             }
       }
}