1. Lecture 17: Animation Yoni Fridman 7/27/01 7/27/01

2. OutlineOutline ä Applet methods  The init() method  The start() and stop() methods  The run() method  The repaint() method ä Threads  The sleep() method ä Fun examples ä Applet methods  The init() method  The start() and stop() methods  The run() method  The repaint() method ä Threads  The sleep() method ä Fun examples

3. Applet Methods  We’ve seen the paint() method of the Applet class – it’s used to display stuff to the screen.  When is the paint() method called? ä Automatically when the applet is first displayed on the screen. ä Automatically when the window containing the applet is resized. ä Automatically when the applet becomes visible after having been covered by another window. ä Whenever the applet needs to be refreshed for animation purposes.  The paint() method can be called a huge number of times. We don’t want to put all of our code in this method – that would slow down the program.  We’ve seen the paint() method of the Applet class – it’s used to display stuff to the screen.  When is the paint() method called? ä Automatically when the applet is first displayed on the screen. ä Automatically when the window containing the applet is resized. ä Automatically when the applet becomes visible after having been covered by another window. ä Whenever the applet needs to be refreshed for animation purposes.  The paint() method can be called a huge number of times. We don’t want to put all of our code in this method – that would slow down the program.

4. The init() Method  Another method of the Applet class is the init() method.  Like the paint() method, this method is also called automatically.  The paint() method is called repeatedly.  The init() method only gets called once, when the applet is first loaded into the web browser.  Any initialization code that can go in the init() method rather than the paint() method should.  For example, setBackground() should go in the init() method.  Another method of the Applet class is the init() method.  Like the paint() method, this method is also called automatically.  The paint() method is called repeatedly.  The init() method only gets called once, when the applet is first loaded into the web browser.  Any initialization code that can go in the init() method rather than the paint() method should.  For example, setBackground() should go in the init() method.

5. The start() and stop() Methods  The start() method gets called automatically when the applet becomes active (for example, when the web page is refreshed).  The stop() method gets called automatically when the applet becomes inactive (for example, when you go to a different web page). ä There’s certain code that’s required in these methods (see examples). Normally, you won’t want to add any additional code to them.  The start() method gets called automatically when the applet becomes active (for example, when the web page is refreshed).  The stop() method gets called automatically when the applet becomes inactive (for example, when you go to a different web page). ä There’s certain code that’s required in these methods (see examples). Normally, you won’t want to add any additional code to them.

6. The run() Method  The run() method gets called between the start() and stop() methods.  Normally there’s a loop inside this method, and the paint() method is called from inside the loop.  This repeated calling of the paint() method, where the stuff being painted is slightly different each time, is what produces an animation.  run() is not an instance method of the Applet class. To use it, we have to add something else to our class definition: ä public class Animation extends Applet implements Runnable  The run() method gets called between the start() and stop() methods.  Normally there’s a loop inside this method, and the paint() method is called from inside the loop.  This repeated calling of the paint() method, where the stuff being painted is slightly different each time, is what produces an animation.  run() is not an instance method of the Applet class. To use it, we have to add something else to our class definition: ä public class Animation extends Applet implements Runnable

7. The repaint() Method  Actually, we don’t usually call the paint() method.  Rather, we call the repaint() method.  paint() will simply display graphics on top of what’s already there.  repaint(), on the other hand, clears the graphics context first. It then calls paint().  Actually, we don’t usually call the paint() method.  Rather, we call the repaint() method.  paint() will simply display graphics on top of what’s already there.  repaint(), on the other hand, clears the graphics context first. It then calls paint().

8. Threads and the sleep() Method ä A thread is a single execution of a program. ä Some languages, including Java, allow for multiple threads to run at once. ä That is, you can have multiple program executions going at once.  Thread.sleep() tells your execution to sleep, or pause, so that other executions can have a turn.  Thread.sleep() takes one argument of type int, indicating how many milliseconds to pause for.  Example: Thread.sleep(1000) will pause your program for 1 second. ä A thread is a single execution of a program. ä Some languages, including Java, allow for multiple threads to run at once. ä That is, you can have multiple program executions going at once.  Thread.sleep() tells your execution to sleep, or pause, so that other executions can have a turn.  Thread.sleep() takes one argument of type int, indicating how many milliseconds to pause for.  Example: Thread.sleep(1000) will pause your program for 1 second.

9. HomeworkHomework ä HW7 out today, due Tuesday. ä Tic-Tac-Toe. ä HW7 out today, due Tuesday. ä Tic-Tac-Toe.