ITEC 120 2008spring ibarland, jdymacek

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lect07c
Objects as fields
Dogs and Kennels

Consider a class Dog, which has this interface. Could you write this class? Sure you could! (If not, it'd be a great practice problem.)

Go ahead an make several Dogs in BlueJ; declare and initialize the variables from Code Pad. You may use (the test fixture from) this .jar file (see how to get .jar files into BlueJ).

Dog myDog;
myDog = new Dog( "rex", 5 );

Dog movieStar;
movieStar = new Dog( "Air Bud", 3 );

Now we want to represent another, second class: Kennel. In our model, every Kennel has an address, and two Dogs being boarded. In addition, it seems that every kennel also has a third resident dog who is fifteen and is named “Bowser”.

Write a class to represent kennels. What do its setters/getters look like? What does its constructor look like? Write it!

Kennel a1Doggies;
a1Doggies = new Kennel( "123 puppy lane", movieStar, myDog );

the environment:                    The object bench (the “heap”)
                                                                       Dog
            +--------+                                                 +------------------------+
___myDog___ |    *---|---------------------------------------------->  |           ___________  |            
            +--------+                                                 | name     | "rex"     | |
                               Dog                                     |           -----------  |
                               +------------------------+              |           ___________  |
                               |           ___________  |              | age      |____5______| |
            +--------+         | name     | "Air Bud" | |           /->|           ___________  |
_movieStar_ |    *---|------>  |           -----------  |           |  | sound    | "woof"    | |
            +--------+         |           ___________  |           |  |           -----------  |
                               | age      |____3______| |           |  +------------------------+
                         /-->  |           ___________  |           |
                         |     | sound    | "woof"    | |           |       
                         |     |           -----------  |           |       
                         |     +------------------------+           |       
                         |                                          |       Dog                                  
                         |                                          |       +------------------------+
                         |                                          |       |           ___________  |
                         |                                          |       | name     | "Bowser"  | |
                         |                                          |       |           -----------  |
                         |                                          |       |           ___________  |
                         |                                          |   /-> | age      |___15______| |
                         \--------------------------------------\   |   |   |           ___________  |
                                                                |   |   |   | sound    | "woof"    | |
                                                                |   |   |   |           -----------  |
                              Kennel                            |   |   |   +------------------------+        
                              +-----------------------------+   |   |   |
            +--------+        |           _________________ |   |   |   |
_a1Doggies_ |    *---|------> | address  | "123 Puppy Lane"||   |   |   |
            +--------+        |           ----------------- |   |   |   |
                              |           ___________       |   |   |   |
                              | dog1     |     *-----|------|---/   |   |
                              |           -----------       |       |   |
                              |           ___________       |       |   |
                              | dog2     |     *-----|------|-------/   |
                              |           -----------       |           |            
                              |           ___________       |           |
                              | resident |     *-----|------|-----------/
                              |           -----------       |
                              +-----------------------------+

• How many objects are created (that is, how many times was new called?)                 
• How many local variables are there?                 
• What is the type of a1Doggies?                 
• What is the type a1Doggies.getAddress()?                 
• What is (the value of) a1Doggies.getAddress()?                 
• What is the type a1Doggies.getDog1()?                 
• What is (the value of) a1Doggies.getDog1()?                 
• Note that a Kennel does not keep track of the ages/names of its Dogs: it only keeps track of which Dogs it has; each Dog keeps track of its own age/name.
• How do you find out what the age of the first dog in a1Doggies is?                 

To consider: How to write a function so that people can ask any Kennel “what is the average age of the three Dogs you contain?”?

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©2008, Ian Barland, Radford University Last modified 2008.Jan.24 (Thu)

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