Thursday, March 15, 2012

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.
  4. 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;
     }
            
  5. (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.

4 comments:

Anonymous said...

Is it just me, or are the answers for Questions 1 not shown?

Jose Vidal said...

You're right. You can run the program to see what it prints out. I'll add them later.

Anonymous said...

Problem is for Question 1, for the public class Ship, the class Sailboat isn't included

Jose Vidal said...

Ah, yes, the one I had to write on the board. I'll add it now.