Timing

To do animation or anything that requires delay, you need to implement the class runnable. The code is a little complex; it uses something called threads to delay operating. You dont need to understand the code. All you need to do is implement runnable in your code decleration, and include the code below the **********************.

• The only editable section of that code is the int delay which is in millliseconds.
• When the applet is run, the delay is started automatically and paint is called every 50 milliseconds.
• To stop the applet, call the method stop()

// This class is to test animation // Designed by Jeff Borland // Date 11:16:06 import java.awt.*; import java.applet.*; public class TestAnimation extends Applet implements Runnable { int x=0; public void paint (Graphics g) { //The following two lines resets the screen g.setColor(Color.white); g.fillRect(0,0,500,500); //Seting color to black in order for text to be black g.setColor(Color.black); //incrementing x, so each time the animation is called, the text moves along x++; g.drawString("a", x,10); //when x finally reaches 100 pixels, stop the animation. if (x==100)stop(); } /*********************************************************************************************/ /* BELOW IS FOR ANIMATION. THE ONLY THING THAT YOU NEED TO CHANGE IS DELAY */ int frame; int delay=50; // this is the time of the delay in milliseconds. Thread animator; public void update(Graphics g) { paint(g); } /** * This method is called when the applet becomes visible on * the screen. Create a thread and start it. */ public void start() { animator = new Thread(this); animator.start(); } /** * This method is called by the thread that was created in * the start method. It does the main animation. */ public void run() { // Remember the starting time long tm = System.currentTimeMillis(); while (Thread.currentThread() == animator) { // Display the next frame of animation. repaint(); try { tm += delay; Thread.sleep(Math.max(0, tm - System.currentTimeMillis())); } catch (InterruptedException e) { break; } // Advance the frame frame++; } } /** * This method is called when the applet is no longer * visible. Set the animator variable to null so that the * thread will exit before displaying the next frame. */ public void stop() { animator = null; } }

Assignment:

1. Add code so that every 40 times it moves the color changes between green and red.
2. Add code so that when they press 1-3 the animation changes speed. (change the delay - which already is a global variable)
3. You will need to add the keylistener stuff. (implement runnable, KeyListener (remember to have nec. imports and init statement).
4. Add code so when space bar is pressed the animation starts and stops.