Speed Control

The files SpeedControl.java and SpeedControlPanel.java contain an applet (and its associated panel) with a circle that moves on the panel and rebounds from the edges. (NOTE: the program is derived from Listing 8.19 and 8.20 in the text. You may have used the Circle class in Circle.java in an earlier lab on animation.) Save the program to your directory and run it in the appletviewer (you may use the file Speed.html) to see how it works.

In this lab exercise you will add to the panel a slider that controls the speed of the animation. Study the code in ViewSliderPanel.java (Listing 9.17 in the text) to help understand the steps below.

1. Set up a JSlider object. You need to
   • Declare it.
   • Instantiate it to be a JSlider that is horizontal with values ranging from 0 to 200, initially set to 30.
   • Set the major tick spacing to 40 and the minor tick spacing to 10.
   • Set paint ticks and paint labels to true and the X alignment to left.

2. Set up the change listener for the slider. A skeleton of a class named SlideListener is already in SpeedControlPanel.java. You need to
   • Complete the body of the statedChanged function. This function must determine the value of the slider, then set the timer delay to that value. The timer delay can be set with the method setDelay (int delay) in the Timer class.
   • Add the change listener to the JSlider object.

3. Create a label ("Timer Delay") for the slider and align it to the left.

4. Create a JPanel object and add the label and slider to it then add your panel to the SOUTH of the main panel (note that it has already been set up to use a border layout).

5. Compile and run the applet. Make sure the speed is changing when the slider is moved. (NOTE: Larger delay means slower!)

6. You should have noticed one problem with the applet. The ball (circle) goes down behind the panel the slider is on. To fix this problem do the following:
   • In actionPerformed, declare a variable slidePanelHt (type int). Use the getSize() method to get the size (which is a Dimension object) of the panel you put the slider on. Assign slidePanelHt to be the height of the Dimension object. For example, if your panel is named slidePanel the following assignment statement is what you need:

             slidePanelHt = slidePanel.getSize().height;
     

   • Now use this height to adjust the condition that tests to see if the ball hits the bottom of the panel.
   • Test your program to make sure it is correct.