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KING ABDULAZIZ UNIVERSITY

Faculty of Computing & Information Technology

Department of Computer Science

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Lab Manual

CPCS203

Programming II

(Object-oriented)

1432/1433H

Lab - 8
$e:\kau\cpcs courses\lab sildes\java[1]_small.png$ ^{Learning Procedure}

Stage J (Journey inside-out the concept)
Stage a₁ (apply the learned)
Stage v (verify the accuracy)
Stage a₂ (assess your work)

Laboratory 8:

Statement Purpose:

This lab will give you practical using of Arrays in java.

Activity Outcomes:

This lab teaches you the following topics:

Manipulate a collection of data values, using an array.
Declare and use an array of primitive data types in writing a program.
Declare and use an array of objects in writing a program
Define a method that accepts an array as its parameter and a method that returns an array
Describe how a two-dimensional array is implemented as an array of arrays

Instructor Note:

As pre-lab activity, read Chapter 10 from the book (An Introduction to Object-Oriented Programming with Java, 4th Edition by C. THOMAS WU (Book’s website www.mhhe.com/wu), and also as given by your theory instructor.

Names I.D.

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Stage J (Journey)

Introduction

Single-dimensional arrays: is a container object that holds a fixed number of values of a single type. The length of an array is established when the array is created. After creation, its length is fixed.

Example: An array of ten elements

Each item in an array is called an element, and each element is accessed by its numerical index. As shown in the above illustration, numbering begins with 0. The 9th element, for example, would therefore be accessed at index 8.

Multi-dimensional arrays: are usually represented in a row-column approach on paper, and the terms "rows" and "columns" are used in computing.

Declare a 2-dimensional array as follows:

int[][] a2; // Declares, but doesn't allocate, 2-dim array.

Allocation:

As with all arrays, the new keyword must be used to allocate memory for an array. For example

int[][] a2 = new int[10][5];

This allocates an int array with 10 rows and 5 columns.

Processing 2-dimensional arrays:

Often 2-dimensional arrays are processed with nested for loops. Notice in the following example how the rows are handled as separate objects. For example,

int[][] a2 = new int[10][5];

// print array in rectangular form

for (int r=0; r

for (int c=0; c

System.out.print(" " + a2[r][c]);

}

System.out.println("");

}

Stage a₁ (apply)

Lab Activities:

Activity 1:

Declaring and Creating Arrays:

You can declare and create an array by using the following syntax:

data type [ ] arrayname = new data type[size of array]

Where data type may be int, float, long, double, string etc.

And size of array is the size (No of data you want to store).

Processing Arrays:

Here are some examples of processing arrays:

(Initializing arrays with random values) The following loop initializes the array myList with random values between 0.0 and 99.0:

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

myList[i] = Math.random() * 100;

}

(Printing arrays) To print an array, you have to print each element in the array using a loop like the one shown below.

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

System.out.print(myList[i] + " ");

}

(Summing all elements) Use a variable named total to store the sum. Initially total is 0. Add each element in the array to total, using a loop like this:

double total = 0; for (int i = 0; i < myList.length; i++) {

total += myList[i];

}
Example 1.1: A program in java to first read the numbers and store them in an array, then find the largest number in the array, and finally count the occurrences of the largest number in the array.

import javax.swing.JOptionPane;

public class TestArray {

/** Main method */

public static void main(String[] args) {

final int TOTALNUMBERS = 6;

int[] numbers = new int[TOTALNUMBERS];

// Read all numbers

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

String numString = JOptionPane.showInputDialog( "Enter a number:");

// Convert string into integer

numbers[i] = Integer.parseInt(numString);

}

// Find the largest

int max = numbers[0];

for (int i = 1; i < numbers.length; i++) {

if (max < numbers[i])

max = numbers[i];

}

// Find the occurrence of the largest number

int count = 0;

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

if (numbers[i] == max) count++;

}

// Prepare the result

String output = "The array is ";

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

output += numbers[i] + " "; }

output += "\nThe largest number is " + max;

output += "\nThe occurrence count of the largest number "

+ "is " + count;

// Display the result

JOptionPane.showMessageDialog(null, output);

} }

Task 1.1: trace out the above code and write the excepted output?

Example 1.2:

public class Demo {

public static void main (String [] args) {

int [] a;

a = new int[4];

a[0] = 3;

for (int i = 1; i < 4; i++)

a[i] = a[0];

a[1] = 6;

for (int i = 0; i < 4; i++)

System.out.println(a[i]);

}

Activity 2:

How to create arrays of objects:

It is possible to create arrays of objects. These may have one or multiple dimensions. To create follow below steps.

Declare an array of object.
Allocate memory for the array elements

Syntax to create Arrays of Objects

className ObjectName[ ] = new className[size];

className is a name of class for which you want to create array of object.

ObjectName is a Object name given to array of object.

Note: Provide integer value in place of size to define size of number of elements in array of object.

Example 2.1: Demonstrate the use of arrays of the objects

class Employee

{

private String name;

protected float billingRate;

public Employee(String name, float billingRate)

{

this.name = name;

this.billingRate = billingRate;

}

public float CalculateCharge(float hours)

{

return(hours * billingRate);

}

public String TypeName()

{

return("Employee");

}

}
public class TestEmployee {

/**

* @param args the command line arguments

public static void main(String[] args) {

Employee[] earray = new Employee[2];

earray[0] = new Employee("A", 15.50F);

earray[1] = new Employee("B", 40F);

System.out.println("{0} charge = {1}" + earray[0].TypeName()+"\t"+ earray[0].CalculateCharge(2F));

System.out.println("{0} charge = {1}"+ earray[1].TypeName()+"\t"+earray[1].CalculateCharge(0.75F));

}

Activity 3:

Passing Arrays to Methods:

To pass an array argument to a method, specify the name of the array without any brackets. For example, if array hourlyTemperatures is declared as

double hourlyTemperatures[] = new double[ 24 ];

then the method call

modifyArray( hourlyTemperatures );
Example 3.1: Example showing Passing Arrays to Methods

Create a Main class and name it as PassArray.
Declare and create array of size ten integer.
Create object of Scanner class
Allow user to enter array data.
Print the array
Call the Max method to display Maximum number among the given array.
Copy the max method as it is outside the main() method.

public static int max(int[] t) {

//1. Assign the first (or any) array element to the variable that will hold //the maximum value.

// Loop through the remaining array elements, starting at the second //element (subscript 1).

//When a larger value is found, that becomes the new maximum.

// ============max

int maximum = t[0]; // start with the first value

for (int i=1; i

if (t[i] > maximum) {

maximum = t[i]; // new maximum

} } return maximum;

}//end method max
Example 3.2: To find the Median of an array:

This method computes the median (middle) value of an array. The array must be sorted before calling this method. It returns the middle element, or the average of the two middle elements if there are an even number of elements.

public static double median(double[] m) {

int middle = m.length/2; // subscript of middle element

if (m.length%2 == 1) {

// Odd number of elements -- return the middle one.

return m[middle];

} else {

// Even number -- return average of middle two

// Must cast the numbers to double before dividing.

return (m[middle-1] + m[middle]) / 2.0;

}

}//end method median

Task 3.1:

Create a Main class and name it as PassArraymedian.

Declare and create array of size ten integers.
Create object of Scanner class
Allow user to enter array data.
Print the array
Call the median method to display median number among the given array.

Example 3.3: The example contains two methods for swapping elements in an array. The first method, named swap, fails to swap two int arguments. The second method, named swapFirst-TwoInArray, successfully swaps the first two elements in the array argument

public class TestPassArray {

/** Main method */

public static void main(String[] args) {

int[] a = {1, 2};

// Swap elements using the swap method

System.out.println("Before invoking swap");

System.out.println("array is {" + a[0] + ", " + a[1] + "}");

swap(a[0], a[1]);

System.out.println("After invoking swap");

System.out.println("array is {" + a[0] + ", " + a[1] + "}");

// Swap elements using the swapFirstTwoInArray method

System.out.println("Before invoking swapFirstTwoInArray");

System.out.println("array is {" + a[0] + ", " + a[1] + "}");

swapFirstTwoInArray(a);

System.out.println("After invoking swapFirstTwoInArray");

System.out.println("array is {" + a[0] + ", " + a[1] + "}");

}

/** Swap two variables */

public static void swap(int n1, int n2) {

int temp = n1;

n1 = n2;

n2 = temp;

}

/** Swap the first two elements in the array */

public static void swapFirstTwoInArray(int[] array) {

int temp = array[0];

array[0] = array[1];

array[1] = temp;

}

}
Activity 4:

Using 2D-array:

Example7: The Rainfall class shows how we can test our array algorithms. It creates the rainfall array in the main () method. It then initializes the array and prints out average daily rainfall and average daily rainfall for the month of March. However, note that we have made a slight modification to the initRain() method. Instead of just assigning 0 to each element, we assign a random value between 0 and 2.0:

rain[month][day] = Math.random() * 2.0;

Note: The Math.random() method can be used to generate numeric test data when large amounts of data are required. The data can be scaled to fit within the expected range of the actual data.

public class Rainfall {

/**

* Initializes the rainfall array

* @ param rain is a 2D-array of rainfalls

* Pre: rain is non null

* Post: rain[x][y] == 0 for all x,y in the array

* Note that the loops use unit indexing.

public void initRain(double rain[][]) {

for (int month = 1; month < rain.length; month++)

for (int day = 1; day < rain[month].length; day++)

rain[month][day] = Math.random() * 2.0; // Random rainfall

} // initRain()

/**

* Computes average daily rainfall for a year of rainfall data

* @ param rain is a 2D-array of rainfalls

* @ return The sum of rain[x][y] / 356

* Pre: rain is non null

* Post: The sum of rain / 365 is calculated

* Note that the loops are unit indexed

public double avgDailyRain(double rain[][]) {

double total = 0;

for (int month = 1; month < rain.length; month++)

for (int day = 1; day < rain[month].length; day++)

total += rain[month][day];

return total/365;

} // avgDailyRain()

/**

* Computes average daily rainfall for a given month containing nDays

* @ param monthRain is a 1D-array of rainfalls

* @ param nDays is the number of days in monthRain

* @ return The sum of monthRain / nDays

* Pre: 1 <= nDays <= 31

* Post: The sum of monthRain / nDays is calculated

public double avgRainForMonth(double monthRain[], int nDays) {

double total = 0;

for (int day = 1; day < monthRain.length; day++)

total = total + monthRain[day];

return total/nDays;

} // avgRainForMonth()
public static void main(String args[]) {

double rainfall[][] = new double[13][32];

Rainfall data = new Rainfall();

data.initRain(rainfall);

System.out.println("The average daily rainfall = "

+ data.avgDailyRain(rainfall));

System.out.println("The average daily rainfall for March = "

+ data.avgRainForMonth(rainfall[3],31));

} // main()

} // Rainfall class

Stage v (verify)

Home Exercises:

Indicate true or false for the following statements:

Every element in an array has the same type.
The array size is fixed after it is declared.
The array size is fixed after it is created.
The elements in an array must be of primitive data type.

Which of the following statements are valid array declarations?

int i = new int(30);

double d[] = new double[30];

char[] r = new char(1..30);

int i[] = (3, 4, 3, 2);

float f[] = {2.3, 4.5, 6.6};

char[] c = new char();

Identify and fix the errors in the following code:

public class Test {

public static void main(String[] args) {

double[100] r;

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

r(i) = Math.random * 100;

} }

Write a program that reads ten numbers, computes their average, and finds out how many numbers are above the average.
Write a program that reads ten integers and displays them in the reverse of the order in which they were read.
Write a program that reads an unspecified number of scores and determines

how many scores are above or equal to the average and how many scores are below the average. Enter a negative number to signify the end of the input. Assume that the maximum number of scores is 100.

Write a method that finds the smallest element in an array of integers.

Use {1, 2, 4, 5, 10, 100, 2, –22} to test the method.

Write a method that sums all the integers in a matrix of integers.

Use {{1, 2, 4, 5}, {6, 7, 8, 9}, {10, 11, 12, 13}, {14, 15, 16, 17}} to test the

method.

Write a method that sums all the integers in the major diagonal in a matrix of integers. Use {{1, 2, 4, 5}, {6, 7, 8, 9}, {10, 11, 12, 13}, {14, 15, 16, 17}} to test the method.
Write a method that sums all the integers in the row 1 and column 2 in a

matrix of integers. Use {{1, 2, 4, 5}, {6, 7, 8, 9}, {10, 11, 12, 13}, {14, 15,

16, 17}} to test the method.

(Airline Reservations System)

A small airline has just purchased a computer for its new automated reservations system. You have been asked to develop the new system. You are to write an application to assign seats on each flight of the airline's only plane (capacity: 10 seats).

Your application should display the following alternatives: Please type 1 for First Class and Please type 2 for Economy. If the user types 1, your application should assign a seat in the first-class section (seats 15). If the user types 2, your application should assign a seat in the economy section (seats 610). Your application should then display a boarding pass indicating the person's seat number and whether it is in the first-class or economy section of the plane.

Use a one-dimensional array of primitive type boolean to represent the seating chart of the plane. Initialize all the elements of the array to false to indicate that all the seats are empty. As each seat is assigned, set the corresponding elements of the array to true to indicate that the seat is no longer available.

Your application should never assign a seat that has already been assigned. When the economy section is full, your application should ask the person if it is acceptable to be placed in the first-class section (and vice versa). If yes, make the appropriate seat assignment. If no, display the message "Next flight leaves in 3 hours."

Stage a₂ (assess)

Lab Report:

The laboratory report of this lab (and also all the following labs in this manual) should include the following items/sections:

A cover page with your name, course information, lab number and title, and date of submission.
A summary of the addressed topic and objectives of the lab.
Implementation: a brief description of the process you followed in conducting the implementation of the lab scenarios.
Results obtained throughout the lab implementation, the analysis of these results, and a comparison of these results with your expectations.
Answers to the given exercises at the end of the lab. If an answer incorporates new graphs, analysis of these graphs should be included here.
A conclusion that includes what you learned, difficulties you faced, and any suggested extensions/improvements to the lab.

Note: only a softcopy is required for both homework and report, please do not print or submit a hard copy.

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