Question

Assignment 1: JAVA Classes, Objects, and Constructors

The goal of this assignment is to get you familiar with some of the most used JAVA syntax, as well as constructors objects, objects calling other objects, class and instance attributes and methods. You will create a small program consisting of Musician and Song classes, then you will have Musicians perform the Songs.

Included is a file “Assignment1Tester.java”. Once you have done the assignment and followed all instructions, you should be able to compile and run “Assignment1Tester.java”. If “Assignment1Tester.java” compiles and runs, this does not mean your code is correct. But it will make sure that your public facing interface and member variables have the correct specification.

Make certain all member variables and methods are exactly as requested. We may use automated marking, and if we do and you spell a member variable differently, you will not get the mark. That is why we highly encourage you to compile and run “Assignment1Tester.java”. It will check some of these things for you.

Every question is worth 5 marks.

1. Open the file “Musician.java”. There is a “static final” variable defaultNumberOfKnownSongs that has been initialized to 3. In the Musician class, we will add 3 more instance variables. The first should be called name and should be of typeString. The second should be called knownSongs and it should be an array of type Song. The third should be an int callednumKnownSongs.

2. Write a constructor that takes two arguments, “String name” and “int numberOfSongs”. Have this constructor initializeknownSongs to an array of Song with length numberOfSongs, and initialize the name instance variable to the name String that was passed in through the constructor. You should make use of the this keyword. Write a second constructor for theMusician class with a single argument “String name” that initializes knownSongs to an array of Song with lengthdefaultNumberOfKnownSongs. In both constructors initialize numKnownSongs to zero.

3. Write a public String toString(). If the name = “Slash” and he knows 2 songs, it should return a String “My name is Slash and I know 2 songs.”

4. Open the class “Song.java”. Write three constructors. Write a no-argument constructor that assigns the name “unknown” to the song name and “pop” to genre. Write a constructor that takes a String argument and assigns it to name, and assigns “pop” to genre. Write a constructor that takes two String arguments, the first of which is assigned to name and the second is assigned to genre. Make sure that “name” comes first in the constructor method signature.

5. Write a static method “randomSong()” that returns a Song object with a random name from the songNames array and a random genre from the songGenre array.

6. Write a method “public String toString()” that returns a String object describing the Song. That is, if name = “Paradise City” and genre = “hard rock”, then “public String toString()” should return the String “the hard rock song ‘Paradise City’.”

7. Write a method “equals(Song song)” in the Song class that compares the current Song object to the song variable. It returns true if the two songs have the same name and same genre, and false otherwise.

8. In the Musician class, write a method “public boolean learnSong(Song song)”. It should assign the song argument to the first open position in the knownSongs array. If the array is full it should not change the array and return false. If the array is not full, add the song and return true.

9. In the Musician class, write a method “public boolean playSong(Song song)”. If the song argument is equal to a song in the knownSongs array, then the method should output the Musicians name followed by “performs” followed by the song. For instance, if the Musician is named “Slash” and the song was ‘Paradise City’, it would print “Slash performs the hard rock song ‘Paradise City’.” to the screen and return true. Hint: you can make use of the toString() method of the Song class. If the Song argument is not equal to any Song in the knownSongs array, then this method should print “Slash does not know the hard rock song ‘Paradise City’.” and return false.

10. In the Musician class, write a method “public void playAllKnownSongs()”. This method should play every song in the knownSong array with each song formatted as in Question 9.

Answer 1

/***************************Musician.java*******************************/

public class Musician {

   /*
   * private data field
   */
   private static final int defaultNumberOfKnownSongs = 3;
   private String name;
   private Song[] knownSong;
   private int callednumKnownSongs;

   /**
   *
   * @param name
   * @param numberOfSongs
   */
   public Musician(String name, int numberOfSongs) {
       this.name = name;
       this.callednumKnownSongs = 0;
       this.knownSong = new Song[numberOfSongs];
   }

   /**
   *
   * @param name
   */
   public Musician(String name) {
       this.name = name;
       this.knownSong = new Song[defaultNumberOfKnownSongs];
       this.callednumKnownSongs = 0;
   }

   public static int getDefaultnumberofknownsongs() {
       return defaultNumberOfKnownSongs;
   }

   public String getName() {
       return name;
   }

   public Song[] getKnownSong() {
       return knownSong;
   }

   public int getCallednumKnownSongs() {
       return callednumKnownSongs;
   }

   @Override
   public String toString() {
       return "My name is " + name + " and i know " + callednumKnownSongs + "songs.";
   }

   public boolean learnSong(Song song) {

       if (knownSong.length - 1 == defaultNumberOfKnownSongs) {

           return false;
       } else {

           for (int i = knownSong.length - 1; i > 0; i--) {

               knownSong[i] = knownSong[i - 1];
           }

           knownSong[0] = song;
           return true;
       }
   }

   public boolean playSong(Song song) {

       int flag = 0;
       for (Song song1 : knownSong) {

           if (song1.equals(song)) {

               System.out.println(name + " performs " + song.toString());
               flag = 1;
           }
       }
       if (flag == 1) {

           return true;
       } else {

           return false;
       }
   }

   public void playAllKnownSongs() {

       for (Song song : knownSong) {

           System.out.println(name + " performs " + song.toString());
       }
   }
}
/********************************Song.java**************************/

import java.util.Random;

public class Song {

   private String songName;
   private String genre;

   public Song() {

       this.songName = "unknown";
       this.genre = "pop";
   }

   public Song(String name) {
       this.songName = name;
       this.genre = "pop";
   }

   public Song(String songName, String genre) {
       super();
       this.songName = songName;
       this.genre = genre;
   }

   public static Song randomSong(Song[] songs) {

       Random random = new Random();

       Song song = null;
       int randomIndex = random.nextInt(songs.length);

       for (int i = 0; i < songs.length; i++) {

           song = songs[randomIndex];
       }
       return song;
   }

   @Override
   public String toString() {
       return "The " + genre + " song " + "'" + songName + "'";
   }

   @Override
   public boolean equals(Object arg0) {
       Song other = (Song) arg0;
       if (this.songName.equalsIgnoreCase(other.songName) && this.genre.equalsIgnoreCase(other.genre)) {

           return true;
       } else {

           return false;
       }
   }

}

Please let me know if you have any doubt or modify the answer, Thanks :)