How to prevent if-statement from being executed only once when its condition is first checked?

Question

I have initialized an int variable i = 0. My code has an infinite while loop which is checked immediately when the activity starts. In this loop I need to perform certain tasks after some time interval (e.g. 3 seconds). My code is similar to this:

while(1){
if (System.currentTimeMillis() - learningTime > 3000) {
            learningTime = System.currentTimeMillis();

            i++;
        }
}

Since System.currentTimeMillis() - learningTime > 3000 is true at the beginning of my program execution, i will increment quickly to 1 and later increments will be made every 3 seconds.

How to force i to increment from 0 to 1 in 3 seconds after the activity starts?

Answer 1

Assign to learningTime the System.currentTimeMillis() value so it's 0 > 3000

learningTime = System.currentTimeMillis()

And, anyway you will block the main thread with this code.

That can be an example of Handler

final Handler handler = new Handler();

Runnable runnable = new Runnable() {
    @Override
    public void run()
    {
        handler.postDelayed(this, 3000);
    }
};

handler.postDelayed(runnable, 3000);

Handler class Runnable Handler postDelayed

Anyway, you don't need anymore learningTime and i (?)

Answer 2

You can use a handler to solve this problem so that you don't block the main thread. I'm not sure if this is the ideal implementation though:

private static final long INTERVAL = 3000;//3 seconds
private Handler handler;


protected void onCreate(Bundle b)
{
    super(b);

    handler = new Handler();

    //post an action to execute after an INTERVAL has elapsed.
    handler.postDelayed(new Runnable(){

        public void run(){
            //do your stuff
            doYourStuff();

            //post the event again until a stopCondition is met.
            if(stopCondition==false){
                handler.postDelayed(this,INTERVAL);
            }

        }

    },INTERVAL);
}

Answer 3

As requested in the comments, here is an example of how to use a Handler to delay running some code until a certain amount of time has passed. Define a handler as a variable in your Activity:

Handler handler = new Handler();

Since that handler was created on the UI thread, anything you post to it will also run on the same thread. You can schedule code to run immediately or with a delay. For example:

handler.postDelayed(new Runnable()
{
    public void run()
    {
        //Your code here
    }
}, 3000);   //Code will be scheduled to run on the UI thread afer 3 seconds