About the "onDoubleTap" function in android developer sample "InteractiveChart",

I want to learn how to handle the image and gesture function in android. So I read the sample "InteractiveChart" under "Animating a Scroll Gesture" section in Android developer website. While I read about "onDoubleTap" method in InteractiveLineGraphView.java.

        @Override
        public boolean onDoubleTap(MotionEvent e) {
           mZoomer.forceFinished(true);
           if (hitTest(e.getX(), e.getY(), mZoomFocalPoint)) {
            mZoomer.startZoom(ZOOM_AMOUNT);
           }
           ViewCompat.postInvalidateOnAnimation(InteractiveLineGraphView.this);
           return true;
        }

I checked the code of Zoomer. It mainly calls DecelerateInterpolator method and set some variables. I wonder how can "Zoomer" achieve the double tap zoom function. Does "DecelerateInterpolator" do the work? Or I just missed something?

public class Zoomer {
/**
 * The interpolator, used for making zooms animate 'naturally.'
 */
private Interpolator mInterpolator;

/**
 * The total animation duration for a zoom.
 */
private int mAnimationDurationMillis;

/**
 * Whether or not the current zoom has finished.
 */
private boolean mFinished = true;

/**
 * The current zoom value; computed by {@link #computeZoom()}.
 */
private float mCurrentZoom;

/**
 * The time the zoom started, computed using {@link android.os.SystemClock#elapsedRealtime()}.
 */
private long mStartRTC;

/**
 * The destination zoom factor.
 */
private float mEndZoom;

public Zoomer(Context context) {
    mInterpolator = new DecelerateInterpolator();
    mAnimationDurationMillis = context.getResources().getInteger(
            android.R.integer.config_shortAnimTime);
}

/**
 * Forces the zoom finished state to the given value. Unlike {@link #abortAnimation()}, the
 * current zoom value isn't set to the ending value.
 *
 * @see android.widget.Scroller#forceFinished(boolean)
 */
public void forceFinished(boolean finished) {
    mFinished = finished;
}

/**
 * Aborts the animation, setting the current zoom value to the ending value.
 *
 * @see android.widget.Scroller#abortAnimation()
 */
public void abortAnimation() {
    mFinished = true;
    mCurrentZoom = mEndZoom;
}

/**
 * Starts a zoom from 1.0 to (1.0 + endZoom). That is, to zoom from 100% to 125%, endZoom should
 * by 0.25f.
 *
 * @see android.widget.Scroller#startScroll(int, int, int, int)
 */
public void startZoom(float endZoom) {
    mStartRTC = SystemClock.elapsedRealtime();
    mEndZoom = endZoom;

    mFinished = false;
    mCurrentZoom = 1f;
}

/**
 * Computes the current zoom level, returning true if the zoom is still active and false if the
 * zoom has finished.
 *
 * @see android.widget.Scroller#computeScrollOffset()
 */
public boolean computeZoom() {
    if (mFinished) {
        return false;
    }

    long tRTC = SystemClock.elapsedRealtime() - mStartRTC;
    if (tRTC >= mAnimationDurationMillis) {
        mFinished = true;
        mCurrentZoom = mEndZoom;
        return false;
    }

    float t = tRTC * 1f / mAnimationDurationMillis;
    mCurrentZoom = mEndZoom * mInterpolator.getInterpolation(t);
    return true;
}

/**
 * Returns the current zoom level.
 *
 * @see android.widget.Scroller#getCurrX()
 */
public float getCurrZoom() {
    return mCurrentZoom;
}

}

Can someone also recommend some great sample about image and gesture handling? From basic to advanced.....Thanks a lot.