the ball move to position action_down in android

I have a ball in the screen .I want When I implemented action_down , the ball will move to this position .This my code :
public boolean onTouchEvent(MotionEvent event){

    if(event.getAction()==MotionEvent.ACTION_DOWN){
         x1 = (int) event.getX();
         y1 = (int) event.getY();
 
         float dx = x1-x;
         float dy = y1-y;
         float d = (float)Math.sqrt(dx*dx+dy*dy);
         vx = dx*4/d;
         vy = dy*4/d;
     }
 

}
and onDraw:
protected void onDraw(Canvas canvas) {
canvas.drawColor(Color.BLACK);

    Matrix matrix = new Matrix();
     matrix2.postTranslate(x - bitmap.getWidth()/2, y - bitmap.getHeight()/2);
     x = x+vx ;
     y = y+vy ;
 
     canvas.drawBitmap(bitmap, matrix, null);
 

}

When ,the ball will move to position action_down .But Why the ball was in the position action_down ,it don't stop ?

Please help me?
Thank you?

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