Java: Perform Action Every X Seconds

Question

I've got a working Java program and I would like to draw an object on the display every X seconds. What is the best way to do this? I was thinking of using a for loop and some sleep statements, but I'm curious if there is an easier or more efficient way to go about this.

Thanks.

Answer 1

The simplest way would be to use a javax.swing.Timer

Timer timer = new Timer(X, new ActionListener() {
    public void actionPerformed(ActionEvent evt) {
        // Update the variables you need...
        repaint();
    }
});

timer.setRepeats(true);
timer.setCoalesce(true);
timer.start();

You might also like to have a read through

• The Event Dispatching Thread
• Concurrency in Swing

So you can understand why you should never use a while (true) { Thread.sleep(X) } call in Swing (inside the EDT)

Answer 2

ScheduledExecutorService might help here. The Javadoc shows example usage. Don't forget to call the shutdown method when you're finished.

Answer 3

Using Thread, this will draw a rectangle on the screen every XMilSeconds. This will stop after 5 runs. Edit the xMilSeconds for slower runs, and j > 4 for how many runs before stoping. It does freeze though, that I can't fix.

int i = 0;
private long xMilSeconds = 300;
private boolean paint;
public boolean running = true;

public void paint(Graphics g)
{
    super.paint(g);
    if(paint)
    {
        for(;i < i+1;)
        {
             g.drawRect(i+49,i+49,i+299,i+99);   
             g.setColor(Color.RED);  
             g.fillRect(i+49,i+49,i+299,i+99); 
        }
        paint = false;
    }
}

public void run()
{
    while(running)
    {
        try
        {
            Thread.sleep(xSeconds);
            paint = true;
            repaint();
            i++;
            j++;
            if(j > 4)
            {
                running = false;
            }
        }
        catch(Exception e)
        {
            e.printStackTrace();
        }
    }
}