private void startAnimation () {

    DisplayMetrics metrics = new DisplayMetrics();
    getWindowManager ().getDefaultDisplay ().getMetrics (metrics);

    int width   = metrics.widthPixels;
    int height  = metrics.heightPixels;
    float scale = metrics.density;

    float initLeftX         = leftBall.getX ();
    float initLeftY         = leftBall.getY ();
    float targetLeftX       = (width / 2) - 10;
    float targetLeftY       = (height - outerContainer.getHeight ()) / 2 - 10;

    float initRightX        = rightBall.getX ();
    float initRightY        = rightBall.getY ();
    float targetRightX      = (width / 2) - 10;
    float targetRightY      = (height - outerContainer.getHeight ()) / 2 - 10;

    AnimatorSet animSet     = new AnimatorSet ();

    ObjectAnimator anim1    = ObjectAnimator.ofFloat (leftBall, "x", initLeftX, targetLeftX);
    ObjectAnimator anim2    = ObjectAnimator.ofFloat (leftBall, "y", initLeftY, targetLeftY);
    ObjectAnimator anim3    = ObjectAnimator.ofFloat (rightBall, "x", initRightX, targetRightX);
    ObjectAnimator anim4    = ObjectAnimator.ofFloat (rightBall, "y", initRightY, targetRightY);

    animSet.play (anim1).with (anim2).with (anim3).with (anim4);

    animSet.setDuration (5000);
    animSet.start ();

}