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Ways to Extend the Case Study
• Subclass Fish– Add HungryFish that eat other fish when they are
hungry enough– Add BottomFish that stay on the bottom– Add SickFish that spread disease to neighbors
• Add non-Fish classes– Walls (extend AbstractDrawable)– Snorkelers (extend AbstractActionable)– Dolphins (extend Mammal)
How to Subclass Fish
• Create a new class that extends Fish– Like HungryFish
• Add any fields needed by the new class• Add constructors that call super to initialize the
inherited private fields• Override the act method
– public void act()
• Override generateChild to create this kind of fish– protected void generateChild(Location loc)
• Add any methods needed by act()
Adding Subclasses of Fish
• Edit MBSGUI.java– Add the new class name to fishClassNames
• String[] fishClassNames = {"Fish", "HungryFish", "DarterFish", "SlowFish"};
– Add a way to display the new class• Custom drawn one
DisplayMap.associate("HungryFish", new RoundFishDisplay());
• Gif imageDisplayMap.associate("SlowFish",
new FishImageDisplay("smallfish.gif",
Direction.EAST));
Adding HungryFish
• Add a field to say how hungry this fish is– private int hunger = 0;
• Add a field to say when ready to eat– private static final int NEED_TO_EAT = 5;
• Override the act() method– Increase the hunger each time the method is called– If hungry enough eat a random fish neighbor
• Move to the neighbor’s location and reset hunger to 0
– Otherwise use the inherited move method
Fish and HungryFish
Adding Non-Fish
• The problem is the assumption in many classes that you will only have Fish or subclasses of Fish
• To solve this I needed to change the GUI classes– So use mbsguigt.jar instead of mbsgui.jar in
your classpath– Replace Fish, BoundedEnv, and MBSGUI,
and Simulation
Added Interfaces and Classes
• Interfaces– Drawable inherits from Locatable– Actionable inherits from Drawable
• New Classes– AbstractActionable the class to use to create non-fish
objects that can act() and die()– AbstractDrawable the class to use to create non-fish
objects that don’t act()– DrawableImageDisplay the class to use to display gifs
for non-fish objects
Sample New Classes
• Added a Mammal Class– Need to come to the surface to breathe– Extends AbstractActionable
• Added a Starfish Class– Which drops to the bottom and moves along
the bottom– Extends AbstractActionable
• Added an Orca Class– Extends Mammal
Sample New Classes
Adding Walls
• The Wall class extends AbstractDrawable
• Displayed by WallDisplay which just draws a filled rectangle – extends AbstractDrawableDisplay
• Has an id, location, direction, color, and environment
• Don’t act or die
Walls
Other Ways to Extend
• Change the way things are drawn– Create new classes that extend FishDisplay
like RoundFishDisplay and NarrowFishDisplay
• Reuse classes for Checkers
• Simulate a rat in a maze – Some rats can move randomly– Some rats can go toward the cheese
