CountDown

/**
 * CountDown.java
 * Written By Chuck Cusack
 * October, 2005
 * 
 * A JPanel which displays a countdown.
 * It uses a Thread so that the countdown can be delayed properly.
 * 
 * Note: This is not the only way, and probably not the best way 
 * to accomplish this task, but it seems to work fine.
 */
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class CountDown extends JPanel implements Runnable, ActionListener {
// ActionListener is implemented so that a button click (or whatever) can
//     heard, and we can do our thing here.
// Runnable is implemented so we can create a Thread to execute the 
//     doIt method in such a way that we can create pauses.
    private int currentNumber;
    boolean working=false;
    
    public void paintComponent(Graphics g) {
       g.setColor(Color.black);
       g.fillRect(0,0,200,200);
       g.setColor(Color.red);
       g.drawString(""+currentNumber,100,100);
    }
    
    // From the Runnable interface.  When a thread is create with
    // this Runnable object as a target, it executes this method.
    // We use the variable "working" so that multiple button pushes
    // will be ignored during animation.
    public void run() {
        working=true;
        doIt(30);
        working=false;
    }
    
    // When something invokes the actionPerformed method on this object,
    // it will create a new Thread with this object as the target.
    // Thus, when this method executes, the eventual result is that the
    // run method executes.  Of course, this depends on the value of
    // the "working" variable.
    public void actionPerformed(ActionEvent e) {
        if(!working) {
           new Thread(this).start();
        }
    }
    
    // The recursive algorithm that does all the work.
    // It prints the number n, pauses, and then makes a
    // recursive call.
    public void doIt(int n) {
      // The base case
      if(n<=0) return;
      
      // Change the number and redraw
      currentNumber=n;
      repaint();
      
      // Pause
      try { Thread.sleep(500); }
      catch (InterruptedException e){ }
      
      // The recursive call
      doIt(n-1);
    }
}