CMPSCI 187: Programming With Data Structures

David Mix Barrington

Fall, 2011

Discussion Assignment #4: Hacking Linked Lists

5 October 2011

Last Monday in lecture we began our discussion of linked data structures and reviewed the LinearNode generic class from Section 4.4 of L&C. Today we will play with a class that uses LinearNode objects to describe a sled dog team. Here the class SledDog extends the class Dog from the midterm, where a SledDog object has an additional String field called breed and appropriate get and set methods.

Here is code for LinearNode and some of the code for the classes Dog, SledDog, and DogTeam.

    public class LinearNode {
       private T element;
       private LinearNode next;
       public LinearNode( ) {next = null; element = null;}
       public LinearNode(T elem) {next = null; element = elem;}
       public LinearNode getNext( ) {return next;}
       public void setNext (LinearNode node) {next = node;}
       public T getElement( ) {return element;}
       public void setElement (T elem) {element = elem;}

    public class Dog {
       private String name;
       private int age;
       // get and set methods, two-parameter constructor omitted

    public class SledDog extends Dog {
       private String breed = "Husky";  // default only, can be reset
       // get and set method, three-parameter constructor omitted

    public class DogTeam {
       private LinearNode leadNode;
       private int size;
       // get and set methods, zero-parameter constructor omitted
       public boolean isEmpty( ) {return (leadNode == null);}
       public void addToLead (SledDog newLead) {
          LinearNode newNode = new LinearNode (newLead);
          newNode.setNext (leadNode);
          leadNode = newNode;
          setSize (getSize( ) + 1);}}

Exercises:

Question 1: Write a method public SledDog removeLead( ) for the DogTeam class that removes and returns the lead dog. If the team is empty, your method should return null and not throw an exception. Don't forget to update the size of the team.

Question 2: Write a method public void switchLastTwo that will reverse the order of the last two dogs in the team, if the team has at least two dogs. (If it has zero or one dog the method should do nothing.)

Question 3: Write a method public SledDog removeYoungest( ) for the DogTeam class that removes and returns the dog in the team with the smallest age, taking the first dog of that age if there are more than one. If the team is empty, your method should return null and not throw an exception. Don't forget to update the size of the team.

Question 4: Write a method public int countHuskies ( ) for the DogTeam class that returns the number of dogs in the team whose breed is exactly "Husky". Remember that the .equals method of the String class returns whether the parameter string has the same letters in the same order as the calling string.

Last modified 5 October 2011