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Chapter 8 Inheritance Lab Exercises Topics Lab Exercises Inheritance Exploring Inheritance A Sorted Integer List Test Questions Overriding the equals Method Adapter Classes Extending Adapter Classes Animation Rebound Revisited Count Down Chapter 8 Inheritance 151 Exploring Inheritance File Dog java contains a declaration for a Dog class Save this file to your directory and study it notice what instance variables and methods are provided Files Labrador java and Yorkshire java contain declarations for classes that extend Dog Save and study these files as well File DogTest java contains a simple driver program that creates a dog and makes it speak Study DogTest java save it to your directory and compile and run it to see what it does Now modify these files as follows 1 Add statements in DogTest java after you create and print the dog to create and print a Yorkshire and a Labrador Note that the Labrador constructor takes two parameters the name and color of the labrador both strings Don t change any files besides DogTest java Now recompile DogTest java you should get an error saying something like Labrador java 18 Dog java lang String in Dog cannot be applied to 1 error If you look at line 18 of Labrador java it s just a and the constructor the compiler can t find Dog isn t called anywhere in this file a What s going on Hint What call must be made in the constructor of a subclass b 2 Fix the problem which really is in Labrador so that DogTest java creates and makes the Dog Labrador and Yorkshire all speak Add code to DogTest java to print the average breed weight for both your Labrador and your Yorkshire Use the avgBreedWeight method for both What error do you get Why Fix the problem by adding the needed code to the Yorkshire class 3 Add an abstract int avgBreedWeight method to the Dog class Remember that this means that the word abstract appears in the method header after public and that the method does not have a body just a semicolon after the parameter list It makes sense for this to be abstract since Dog has no idea what breed it is Now any subclass of Dog must have an avgBreedWeight method since both Yorkshire and Laborador do you should be all set Save these changes and recompile DogTest java You should get an error in Dog java unless you made more changes than described above Figure out what s wrong and fix this error then recompile DogTest java You should get another error this time in DogTest java Read the error message carefully it tells you exactly what the problem is Fix this by changing DogTest which will mean taking some things out 152 Chapter 8 Inheritance Dog java A class that holds a dog s name and can make it speak public class Dog protected String name Constructor store name public Dog String name this name name Returns the dog s name public String getName return name Returns a string with the dog s comments public String speak return Woof Chapter 8 Inheritance 153 Labrador java A class derived from Dog that holds information about a labrador retriever Overrides Dog speak method and includes information about avg weight for this breed public class Labrador extends Dog private String color black yellow or chocolate private int breedWeight 75 public Labrador String name this color color String color Big bark overrides speak method in Dog public String speak return WOOF Returns weight public static int avgBreedWeight return breedWeight 154 Chapter 8 Inheritance Yorkshire java A class derived from Dog that holds information about a Yorkshire terrier Overrides Dog speak method public class Yorkshire extends Dog public Yorkshire String name super name Small bark overrides speak method in Dog public String speak return woof DogTest java A simple test class that creates a Dog and makes it speak public class DogTest public static void main String args Dog dog new Dog Spike System out println dog getName says dog speak Chapter 8 Inheritance 155 A Sorted Integer List File IntList java contains code for an integer list class Save it to your directory and study it notice that the only things you can do are create a list of a fixed size and add an element to a list If the list is already full a message will be printed File ListTest java contains code for a class that creates an IntList puts some values in it and prints it Save this to your directory and compile and run it to see how it works Now write a class SortedIntList that extends IntList SortedIntList should be just like IntList except that its elements should always be in sorted order from smallest to largest This means that when an element is inserted into a SortedIntList it should be put into its sorted place not just at the end of the array To do this you ll need to do two things when you add a new element Walk down the array until you find the place where the new element should go Since the list is already sorted you can just keep looking at elements until you find one that is at least as big as the one to be inserted Move down every element that will go after the new element that is everything from the one you stop on to the end This creates a slot in which you can put the new element Be careful about the order in which you move them or you ll overwrite your data Now you can insert the new element in the location you originally stopped on All of this will go into your add method which will override the add method for the IntList class Be sure to also check to see if you need to expand the array just as in the IntList add method What other methods if any do you need to override To test your class modify ListTest java so that after it creates and prints the IntList it creates and prints a SortedIntList containing the same elements inserted in the same order When the list is printed they should come out in sorted order IntList java An unsorted integer list class with a method to add an integer to the list and a toString method that returns the contents of the list with indices public class IntList protected int list protected int numElements 0 Constructor creates an integer list of a given size public IntList int size list new int size Adds an integer to the list If the list is full prints a message and does nothing public void add int value if numElements list length System out println Can t add list is full else list numElements value numElements 156 Chapter 8 Inheritance Returns a string containing the elements of the list with their indices public String toString String returnString for int i 0 i numElements i

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