P1PH

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Chapter 7 Lab

Arrays

Lab Objectives

 Be able to declare and instantiate arrays

 Be able to fill an array using a loop

 Be able to access and process data in an array

 Be able to write a sorting method

 Be able to use an array of objects

Introduction

Everyone is familiar with a list. We make shopping lists, to-do lists, assignment lists,

birthday lists, etc. Notice that though there may be many items on the list, we call the list

by one name. That is the idea of the array, one name for a list of related items. In this lab,

we will work with lists in the form of an array.

It will start out simple with a list of numbers. We will learn how to process the contents

of an array. We will also explore sorting algorithms, using the selection sort. We will

then move onto more complicated arrays, arrays that contain objects.

Task #1 Average Class

Create a class called Average according to the UML diagram.

Average

-data [ ] :int

-mean: double

+Average( ):

+calculateMean( ): void

+toString( ): String

+selectionSort( ): void

This class will allow a user to enter 5 scores into an array. It will then rearrange the data

in descending order and calculate the mean for the data set.

Attributes:

 data[]— the array which will contain the scores

 mean — the arithmetic average of the scores

Methods:

 Average — the constructor. It will allocate memory for the array. Use a for

loop to repeatedly display a prompt for the user which should indicate that user

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should enter score number 1, score number 2, etc. Note: The computer starts

counting with 0, but people start counting with 1, and your prompt should account

for this. For example, when the user enters score number 1, it will be stored in

indexed variable 0. The constructor will then call the selectionSort and the

calculateMean methods.

 calculateMean — this is a method that uses a for loop to access each score

in the array and add it to a running total. The total divided by the number of

scores (use the length of the array), and the result is stored into the mean.

 toString — returns a String containing data in descending order and the

mean.

 selectionSort — this method uses the selection sort algorithm to rearrange

the data set from highest to lowest.

Task #2 Average Driver

1. Create an AverageDriver class. This class only contains the main method.

The main method should declare and instantiate an Average object. The

Average object information should then be printed to the console.

2. Compile, debug, and run the program. It should output the data set from highest to

lowest and the mean. Compare the computer’s output to your hand calculation

using a calculator. If they are not the same, do not continue until you correct your

code.

Task #3 Arrays of Objects

1. Copy the files Song.java (see Code Listing 7.1), CompactDisc.java (see Code Listing 7.2) and Classics.txt (see Code Listing 7.3) from the Student Files or

as directed by your instructor. Song.java is complete and will not be

edited. Classics.txt is the data file that will be used by

CompactDisc.java, the file you will be editing.

2. In CompactDisc.java, there are comments indicating where the missing code is to be placed. Declare an array of Songs, called cd, with a size of 6.

3. Fill the array by creating a new song with the title and artist and storing it in the appropriate position in the array.

4. Print the contents of the array to the console.

5. Compile, debug, and run. Your output should be as follows:

Contents of Classics:

Ode to Joy by Bach

The Sleeping Beauty by Tchaikovsky

Lullaby by Brahms

Canon by Bach

Symphony No. 5 by Beethoven

The Blue Danube Waltz by Strauss

Copyright © 2019 Pearson Education, Inc., Hoboken NJ

Code Listing 7.1 (Song.java)

/*

This class stores data about a song.

*/

public class Song

{

private String title; // The song's title

private String artist; // The song's artist

/**

Constructor

@param title A reference to a String object

containing the song's title.

@param artist A reference to a String object

containing the song's artist.

*/

public Song(String title, String artist)

{

this.title = title;

this.artist = artist;

}

/**

The toString method

@return A String object containing the name

of the song and the artist.

*/

public String toString()

{

return title + " by " + artist + "\n";

}

}

Code Listing 7.2 (CompactDisc.java)

import java.io.*;

/**

This program creates a list of songs for a CD

by reading from a file.

*/

Copyright © 2019 Pearson Education, Inc., Hoboken NJ

public class CompactDisc

{

public static void main(String[] args)throws IOException

{

FileReader file = new FileReader("Classics.txt");

BufferedReader input = new BufferedReader(file);

String title;

String artist;

// ADD LINES FOR TASK #3 HERE

// Declare an array of Song objects, called cd,

// with a size of 6

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

{

title = input.readLine();

artist = input.readLine();

// ADD LINES FOR TASK #3 HERE

// Fill the array by creating a new song with

// the title and artist and storing it in the

// appropriate position in the array

}

System.out.println("Contents of Classics:");

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

{

// ADD LINES FOR TASK #3 HERE

// Print the contents of the array to the console

}

}

}

Code Listing 7.3 (Classics.txt)

Ode to Joy

Bach

The Sleeping Beauty

Tchaikovsky

Lullaby

Brahms

Canon

Bach

Symphony No. 5

Beethoven

The Blue Danube Waltz

Strauss

CompactDisc.java

CompactDisc.java

import  java . io . * ;

/**
   This program creates a list of songs for a CD
   by reading from a file.
*/

public   class   CompactDisc
{
    public   static   void  main ( String []  args ) throws   IOException
    {
       FileReader  file  =   new   FileReader ( "Classics.txt" );
       BufferedReader  input  =   new   BufferedReader ( file );
       String  title ;
       String  artist ;

       // ADD LINES FOR TASK #3 HERE
       // Declare an array of Song objects, called cd,
       // with a size of 6

       for   ( int  i  =   0 ;  i  <  cd . length ;  i ++ )
       {
         title  =  input . readLine ();
         artist  =  input . readLine ();

          // ADD LINES FOR TASK #3 HERE
          // Fill the array by creating a new song with
          // the title and artist and storing it in the
          // appropriate position in the array
       }

       System . out . println ( "Contents of Classics:" );
       for   ( int  i  =   0 ;  i  <  cd . length ;  i ++ )
       {
          // ADD LINES FOR TASK #3 HERE
          // Print the contents of the array to the console
       }
    }
}