Test 2 and Lab Test 2

Here are the Test 2s and the answers:

1. (25%) What does the following program print out when run?
   
   

   public class Boat extends Ship {
   
    private int seaWorthinessRating;
   
    public Boat(double maxSpeed) {
     super(maxSpeed);
     seaWorthinessRating = 33;
    }
   
    public Boat(double maxSpeed, int rating) {
     super(maxSpeed);
     seaWorthinessRating = rating;
    }
   
    public String toString(){
     return "mp=" + maxSpeed + " seaworth=" + seaWorthinessRating;
    }
   
   }
   
   public class SailBoat extends Boat {
   
     public String toString(){
       return "Sailboat";
     }
   }
   
   public class Ship {
   
    protected double maxSpeed;
   
    public Ship(double maxSpeed){
     this.maxSpeed = maxSpeed;
    }
   
    public String toString(){
     return "maxSpeed="  + maxSpeed;
    }
   
    public static void main(String[] args){
     Ship s1 = new Ship(1);
     System.out.println(s1);
     Ship s2 = new Boat(2,66);
     Ship s22 = new Boat(8);
     System.out.println(s2);
     System.out.println(s22);
     SailBoat s3 = new SailBoat(3,77);
     System.out.println(s3);
     Ship s4 = (Ship)s3;
     System.out.println(s4);
    }
   }

   
   
2. (25%) What is wrong with the program below? Explain.
   

   public interface Drinkable {
    public void drink();
   
    public boolean isEmpty(){ return false;}
   }
   
   public class RedBull implements Drinkable {
   
    private int size;
   
    public RedBull(int size){
     this.size = size;
    }
   
    public void drink(){
     System.out.println("Yuuuuuckkkkk");
    }
   
    public boolean isEmpty(){
     return true;
    }
   
   }

   Answer: An interface cannot implement a method.
   
3. (25%) Implement a static method which takes as an argument an array of integers a and returns a new array, lets call it r, where r[0] has the sum of a[0] + a[1], and r[1] has the sum of a[2] + a[3], and so on. You can assume that the length of a is even.
   
Answer:

public static int[] everyOther(int[] a){
  int[] result = new int[a.length/2];
  for (int i = 0; i < a.length; i+=2) {
   result[i/2] = a[i] + a[i+1];
  }
  return result;
 }
        

4. (25%) Take a look at this code:
   

   public class Plant {
   
    private String name;
   
    public Plant(String name){
     this.name = name;
    }
   
    public String getName(){
     return name;
    }
   
    public static void main(String[] args){
     Plant[] garden = new Plant[3];
     garden[0] = new Plant("Vine");
     //Create a Rosemary plant with the name Vanity
     // it will have 1024 leaves by default
     garden[1] = new Rosemary("Vanity");
     //This one will have 2048 leaves
     garden[2] = new Rosemary("Pride", 2048);
   
     for (Plant p: garden){
      System.out.println(p.getName()); //print their names
     }
     //getRosemaries() returns the total number of rosemaries
     //  that have been created.
     System.out.println("There are " + Rosemary.getNumRosemaries()
       + " rosemary plants.");
   
     Rosemary r = new Rosemary("Loathing");
     System.out.println(r.getName());
     System.out.println("There are " + Rosemary.getNumRosemaries()
       + " rosemary plants.");
   
    }
   }
           

   Implement the missing Rosemary class so that when we run the code above it will print:
   

   Vine
   Rosemary:Vanity numLeaves=1024
   Rosemary:Pride numLeaves=2048
   There are 2 rosemary plants.
   Rosemary:Loathing numLeaves=1024
   There are 3 rosemary plants.

   
   See the comments in the code for hints on what the various
   methods and attributes Rosemary must have.

   Answer:
   

   public class Rosemary extends Plant {
   
    private int numLeaves;
   
    private static int numCreated = 0;
   
    public Rosemary(String name) {
     super("Rosemary:" + name );
     numLeaves = 1024;
     numCreated++;
    }
   
    public Rosemary(String name, int numLeaves) {
     super("Rosemary:" + name );
     this.numLeaves= numLeaves;
     numCreated++;
    }
   
    public String getName(){
     return super.getName() + " numLeaves=" + numLeaves;
    }
   
    public static int getNumRosemaries(){
     return numCreated;
    }
   
   
   }

and the other one

1. (25%) What does the following program print out when run?
   
   

   public class Boot extends Shoe {
   
    protected int height;
   
    public Boot(int height){
     super(9);
     this.height = height;
    }
   
    public Boot(int height, int size){
     super(size);
     this.height = height;
    }
   }
   
   public class Ugg extends Boot {
   
    public Ugg(int height, int size) {
     super(height,size);
     height--;
    }
   
    public String toString(){
     return "Ugg size=" + super.toString() + " height=" + height;
    }
   }
   public class Shoe {
   
    private int size;
   
    public Shoe(){
     size = 7;
    }
   
    public Shoe(int size) {
     this.size = size;
    }
   
    public String toString() {
     return "Shoe [size=" + size + "]";
    }
   
    public static void main(String[] args) {
     Shoe s1 = new Shoe();
     System.out.println(s1);
     Boot s3 = new Ugg(7,9);
     System.out.println(s3);
     Boot s4 = new Boot(5,15);
     System.out.println(s4);
     Ugg s5 = new Ugg(9,16);
     System.out.println(s5);
     Boot s6 = (Boot)s5;
     System.out.println(s6);
    }
   }

   
   
2. (25%) What is wrong with the program below? Explain.
   

   public interface Playable{
   
    public void play() {
     super();
    };
   
    public int timeLeft();
   }
   
   public class Media {
   
    protected String title;
   
    public Media(String title){
     this.title = title;
    }
   }
   
   public class Song extends Media implements Playable{
   
    protected int runningTime;
   
    public Song(String name, int runningTime){
     super(name);
     this.runningTime = runningTime;
    }
   
    public void play(){
     System.out.println("Playing....");
    }
   
    public int timeLeft(){
     return runningTime - 10;
    }
   }
           

   Answer: An interface cannot implement a method.
   
   
3. (25%) Implement a static method which takes as an argument an array of integers a and returns a new array, lets call it r, where r[0] contains the sum of a[0] and a[last index in a], r[1] contains the sum of a[1] and a[last index in a minus 1], and so on. You can assume that the length of a is even.
   
   

   Answer:

   public static int[] fold(int[] a){
     int[] result = new int[a.length/2];
     for (int i = 0; i < a.length / 2; i++) {
      result[i] = a[i] + a[a.length - 1 - i];
     }
     return result;
    }
                                       

4. (25%) Take a look at this code:
   

   public interface LeafEater {
             public void eatLeaf();
   }
   
   public class Mammal {
   
    protected int numToes;
   
    protected static int count = 0;
   
    public Mammal(){
     numToes = 5;
     count++;
    }
   
    public String toString(){
     return "Mammal with " + numToes + " toes.";
    }
   
    public static void main(String[] args) {
     Mammal[] animals = new Mammal[4];
     animals[0] = new Mammal();
   
     //Creates a giraffe with 8 toes and height of 10.0 feet.
     animals[1] = new Giraffe();
   
     //Creates a giraffe with 5 toes and height of 14.6 feet.
     animals[2] = new Giraffe(14.6);
   
     //Creates a giraffe with 8 toes and height of 10.0 feet.
     animals[3] = new Giraffe();
     for (Mammal m : animals){
      System.out.println(m);
     }
   
     //getCount() returns the number of Mammals that have been created.
     System.out.println("There are " + Giraffe.getCount() + " mammals");
    }
   }

   
   Implement the missing Giraffe class so that when we run the code above it will print:
   

   Mammal with 5 toes.
   Mammal with 8 toes.-- Giraffe: 10.0 feet.
   Mammal with 5 toes.-- Giraffe: 14.6 feet.
   Mammal with 8 toes.-- Giraffe: 10.0 feet.
   There are 4 mammals

   See the comments in the code for hints on what the various methods and attributes Giraffe must have.
   
   

   Answer:

   public class Giraffe extends Mammal implements LeafEater{
   
    private double height;
   
    public Giraffe(){
     super();
     height = 10;
     numToes = 8;
    }
   
    public Giraffe(double height){
     super();
     this.height = height;
    }
   
    public String toString(){
     return super.toString() + "-- Giraffe: " + height + " feet.";
    }
   
    public static int getCount(){
     return count;
    }
   
    public void eatLeaf() {
     System.out.println("Yummm, leaves are good.");
   
    }
   
   }            

And, here is my solution to the Lab Tests.