In this module we will explore many OOP concepts by examining the program "Ballworld". Download the code for Ballworld here:
To run Ballworld, load the files into DrJava and right-click the BallControl file. Select "Run Document's Main Method" to run the program. From the command line, go to the uppermost Ballworld directory and compile all the files in both the directories ("javac ballworld/*.java" and "javac command/*.java") and then run the program as such: "java ballworld.BallControl". The Make Ball button creates an instance of whatever ABall class is typed into the text field on the left. The "Clear All" button clears any balls of the screen. In a nutshell, the way Ballworld works is akin to a flip-book animation: The BallControl class contains a Timer that "ticks" every 50 milliseconds. Every time the timer ticks, the panel in the BallGUI upon which the balls are to be drawn is requested to repaint itself. When the panel repaints, it also tells the Dispatcher to notify every ABall in the system to update itself. When an ABall updates, it updates any internal values it has (its "state") such as its color, radius, and/or velocity. It then moves its position by an amount corresponding to its velocity and draws ("paints") itself onto the panel. Since this is happening 20 times a second, the balls appear to be moving and/or changing and thus the animation is achieved. The ILambda interface3 enables the BallGUI to communicate in a generic, decoupled manner to the BallControl and the Randomizer class is a utility class that provides methods to produce various random values needed by the system. Much of the code in Ballworld is significantly more sophisticated than what has been covered in the course so far-it will be covered soon, don't worry!
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