Lab 04

In this lab you'll be revising the extraction of class hierarchies from informal descriptions, and they associated java syntax. This lab unit is shorter, as it contains a graded evaluation.

Carnivores and Herbivores

Carefully read through the following requirement description:

• Contractually, all animals are required to be able to consume water and food. All animals must have:
  • a method "drink" (common to all animals, prints "Glug, glug, glug");
  • a method "eat" (implementation varies)
• Animals fall into two sub-categories. They can be either herbivores or carnivores (we assume they can never be both).
  • Herbivores and carnivores share a common implementation for drinking.
  • Herbivores and carnivores do not share a common implementation for eating.
    • Herbivores print "Oooh yummy salad!"
    • Carnivores print "Roar, juicy steak!"
• Only specific animal types must be instantiable (with new). These are:
  • Lion (Carnivore)
  • Tiger (Carnivore)
  • Zebra (Herbivore)
  • Gazelle (Herbivore)

Instructions

Your goal is to translate the above requirements into a hierarchy of java classes. There must not be any code duplication, i.e. methods copy-pasted from one method to the other. List all java files (classes or interfaces) you will need for the above implementation.

Create a new file inheritance.txt

For each class-file indicate whether it is: 1. What kind of class it is: * A standard class * An abstract class * An interface 2. What methods must be specified in the class 3. Whether the class inherits from other classes * If yes which other class, and which keyword is used.

Concept extraction

• Translate the following technical requirements into conceptual java code, based on the concepts seen in class
• The goal is to avoid any code replication (copy-pasted method code across classes).
• Use the UML notation seen in class:

Recap requirements first

For each class-file decide on:
1. What kind of class it is: standard/abstract/interface
2. What methods must be specified in the class
3. Whether the class inherits from elswhere: keyword

Implementing an interface

Notation sample:

classDiagram
    class Interface {
        +foo()
    }

    class Class {
        +foo()
    }

    Interface <|.. Class : implements

main

Extending a class

Notation sample:

classDiagram
class BaseClass {
+bar()
}

    class ChildClass {
        +foo()
    }

    BaseClass <|-- ChildClass : extends

Implementation

After you have elicited a fitting class hierarchy on paper, translate your conceptual solution into an implementation.

• Create the required hierarchy of java classes.
• Ensure there is no code duplication between methods.