Lab 12: Adaptor and Decorator

The goal of this lab is to practice using the Adaptor and Decorator patterns.

1. Initial setup

Copy the current version of the simulation code into your directory. This "current version" uses the strategy pattern for hunting, but the only supported strategy is the RandomStrategy (not the ones you made).

cp /homeemp/tvandrun/pub/245/lab12 .

2. Part I: Adaptor

A. Introduction

Evil Professor NenurdNav has prepared his own version of a predator-prey simulation for Lab 21 of his course CS 542. It is similar to ours conceptually, but all the code is different. It includes a class Snake, which has some interesting behavior:

• Snakes reproduce by laying an egg. It leaves an "egg" in a position, though the egg is invisible and does not prevent other agents (or as Prof NenurdNav calls them, "organisms") from entering that position. After a certain number of cycles, the egg hatches, and a new snake is placed in the position where the egg was. If that space is occupied by something else, the hatchling bites it and it dies, no matter what it is.
• Snakes can kill their predators, by biting them. They cannot eat their predators, though. A predator needs to be careful when attacking a snake.

You like this idea and want to plug this Snake class into our version of the simulation. However, it uses all different interfaces. You must use the adaptor pattern in order to make the Snake class work in our simulation.

B. Setup

Copy all the files from a directory where I've put the alien code. This includes Snake.java and three interfaces that Snake depends on.

cp /homeemp/tvandrun/pub/542/lab21/* .

C. Writing Adaptors

Your task here, after you have looked over the files and gotten a basic feel for how they work, has four parts:

1. The main part is to write an Adapter class for Snake. This class will have to be a subtype of Agent, but it is up to you whether it should be a subclass of Animal.
2. Snake, however, depends on Island instead of AgentGrid and Organism instead of Agent You will need to write an Adaptor for AgentGrid.
3. Similarly for Agent.
4. Finally, you will need to adapt PreyArbitor for the PredatorDeterminer interface. This is trickier because PreyArbitor is used only for static purposes, whereas a Snake expects a PredatorDeterminer object.

D. Testing

To test your changes, you will need to make some modifications to PredPrey.java and predprey.day.

3. Part II: Decorator

Next, add a new feature to the simulation: a disease which infects animals. A diseased animal will act the same way as it would otherwise except that

• after a certain number of cycles, the diseased animal dies
• any member of the same species that comes within one space of the diseased animal gets infected
• for tracing purposes, the diseased animal has a different color

Implement this by writing a class DiseasedAnimal which is a decorator for the Animal abstract class. You will need to modify PredPrey.java to test your changes. You will also (unfortunately) need to change PreyArbitor to deal with diseased animals.

4. Turn in

Turn in a hardcopy of the classes you wrote.