While sending a photograph/audio/video/contact through WhatsApp in Android, we have to use a attach button at the top right corner, clicking on that button makes a circular reveal effect. To show or hide a group of UI elements we called it a Reveal Animation. Android API level 21, introduced ViewAnimationUtils.createCircularReveal() method to achieve this animation.

The ViewAnimationUtils.createCircularReveal(view, cx, cy, initialRadius, 0) method enables you to animate a clipping circle to reveal or hide a view.
view - view to reveal
cx - start X coordinate of reveal
cy - start Y coordinate of reveal
initialRadius - start radius. In most cases - 0
endRadius - depends on your view's bounds

btnRevealEffect.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {

            @Override
            public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
                if (isChecked) {

            // To hide a previously visible view using this effect:

                    // get the center for the clipping circle
                    int cx = (view.getRight() + view.getRight()) / 2;
                    int cy = (view.getTop() + view.getTop()) / 2;

                    // get the initial radius for the clipping circle
                    int initialRadius = view.getWidth();

                    // create the animation (the final radius is zero)
                    Animator anim = null;
                    if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.LOLLIPOP) {
                        anim = ViewAnimationUtils.createCircularReveal(view, cx, cy, initialRadius, 0);
                    }

                    // make the view invisible when the animation is done
                    anim.addListener(new AnimatorListenerAdapter() {
                        @Override
                        public void onAnimationEnd(Animator animation) {
                            super.onAnimationEnd(animation);
                            view.setVisibility(View.INVISIBLE);
                        }
                    });

                    // start the animation
                    anim.start();
                } else {

            // To reveal a previously invisible view using this effect:

                    // get the center for the clipping circle
                    int cx = (view.getRight() + view.getRight()) / 2;
                    int cy = (view.getTop() + view.getTop()) / 2;

                    // get the final radius for the clipping circle
                    int finalRadius = Math.max(view.getWidth(), view.getHeight());

                    // create the animator for this view (the start radius is zero)
                    Animator anim = null;
                    if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.LOLLIPOP) {
                        anim = ViewAnimationUtils.createCircularReveal(view, cx, cy, 0, finalRadius);
                    }

                    // make the view visible and start the animation
                    view.setVisibility(View.VISIBLE);
                    anim.start();
                }

            }
        });