Timer with Pause and Resume Support – Android/Java

The CountDownTimer implementation of Android may not be suitable for all cases as the onTick() method of the CountDownTimer runs on the main/UI thread.

The same could also be achieved using a TimerTask, but we do not have support for Pause/Resume operations when you’re using a Timer and a TimerTask.

The following implementation of a generic Timer runs on a separate thread and hence is most suitable for any operation that does not involve UI updates. It is basically a wrapper around a Runnable scheduled with a ScheduledExecutorService which is part of the java.util.concurrent package. The following is a gist of the core Runnable that handles the tick.

future = execService.scheduleWithFixedDelay(new Runnable() {
	public void run() {
		elapsedTime += Timer.this.interval;
		if (duration > 0) {
			if(elapsedTime >=duration){
}, 0, interval, TimeUnit.MILLISECONDS);

For pause, we cancel the Future instance that we obtained when we scheduled the Runnable using the ExecutorService.


For resume, we just schedule the same Runnable again.

We leave the following methods as abstract, to force the classes extending the Timer class to override them.

*	This method is called periodically with the interval set as the delay between subsequent calls.
	protected abstract void onTick();

* This method is called once the timer has run for the specified duration. If the duration was set as infinity, then   * this method is never called.
	protected abstract void onFinish();

Following is an example implementation of a concrete class extending the abstract Timer:

public class ExampleTimer extends Timer{

	public ExampleTimer() {

	public ExampleTimer(long interval, long duration){
		super(interval, duration);

	protected void onTick() {
		System.out.println("onTick called!");

	protected void onFinish() {
		System.out.println("onFinish called!");


Following is a simple test showing the usage of the Timer.

//This creates a timer which will tick every second indefinitely.
Timer oneSecondInfiniteTimer = new ExampleTimer();

//This creates a timer which ticks every 2 seconds, and runs for 20 seconds.
Timer twoSecondTimer = new ExampleTimer(2000l, 20000l);

//Start the timer.

//Pause the timer.

//Resume the timer

The whole code is hosted in GitHub (https://github.com/c05mic/pause-resume-timer ) for your copy-pasting pleasure. 🙂

Contributions are welcome!


Generic N-ary Tree implementation in Java

I needed a simple implementation of a Generic N-ary tree in Java with some useful utility methods for my work, and to my surprise I couldn’t find a simple library that will do the job. So I went ahead and wrote it myself.

You can find it here: https://github.com/c05mic/GenericN-aryTree . Please “star” the repository if you find it useful. 🙂

Features methods:

  • To check if a node exists in the tree.
  •  To find the total number of nodes in the tree
  • To find the total number of descendants of any node in the tree.
  •  To get all the paths from the root to all the leaves as an ArrayList.
  •  To get the longest path from the root to any leaf.
  •  To get the pre-order/post-order traversal path as an ArrayList.

Contributions are welcome!

Activity as a Dialog – Android

It’d be cool to have an Activity to be shown like a Dialog, with the previous activity still in the background.

It turns out that this can easily be done, making use of the android:theme attribute in your activity tag in the AndroidManifest.xml file.

 android:theme="@style/CustomDialog" >

where CustomDialog is a style that we declare in styles.xml (which should go into the res/values folder). Put the following inside the styles.xml.

<?xml version="1.0" encoding="utf-8"?>

<style name="CustomDialog" parent="@android:style/Theme.Dialog">
 <item name="android:windowBackground">@color/transparent</item>
 <item name="android:windowIsFloating">true</item>
 <item name="android:windowNoTitle">true</item>


Start your activity, as you normally would, using startActivity(Intent intent).

Animating an image using Path and PathMeasure – Android

Animating an image along a predefined path (be it a line or a curve) is a common situation that game developers face. Instead of doing it the usual way (Finding the equation of the path, substituting x and finding y values and then using the co-ordinates [x,y] for the animation), we can do this in a more simpler way by making use of Path and PathMeasure.

If you already have a game loop running with its update and render cycles, the following code can easily be implemented. If you’re new to game loops, Obviam.net explains the concept behind game loops in a very concise manner.

Suppose, I want to move an image in a straight line from (0,0) to, say, (100, 100).

Following is a code snippet that shows you how to do it:

Declare the variables that we’d be using:

Path path;
PathMeasure measure;
float[] pos, tan;
float speed, distance;

Initialize your Path object and other variables that we’d be using later on. You could do this on your surfaceCreated() callback if you are using a SurfaceView.

// Init the Path.
 path=new Path();

// Set the starting position of the path to (0,0).

// Add a line to the Path, starting from (0,0), ending at (100, 100).

// Create a PathMeasure object, passing in the Path object
 // we created and a boolean that specifies if the Path should
 // be forced to a closed path.
 measure = new PathMeasure(path, false);

// Here, we're dividing the whole length of the path by 30.
 speed = measure.getLength() / 30;

pos=new float[2];
 tan=new float[2];

The concept behind the moving of the image is simple: Staring at (0,0), in every update cycle, we find a point along the defined path, traversing a little each time.
Now inside the update() method of our game loop, we’d be doing the following:

 public void update()
 while(distance < measure.getLength())

    // getPosTan pins the distance along the Path and
 // computes the position and the tangent.
 measure.getPosTan(distance, pos, tan);

     distance += speed;   // Traversal

Now to render,

 public void render(Canvas canvas)

    //Draw the bitmap on the canvas, passing in the
 //Bitmap object, the x and y co-ordinate and a
 // Paint object.
 canvas.render(bmpImage, pos[0], pos[1], null);

Here the speed directly determines the speed of the animation. Playing with that value, you can arrive at your desired speed.

Just like a line, you can also use curves, Bezier curves, arcs, etc., and a combination of these as well.

Hope this helps!