programming lecture 9

8/3/2019 Programming Lecture 9

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Java Programming: From Problem Analysis to Program Design, 3e 2

Chapter Objectives Learn about arrays

Explore how to declare and manipulate datainto arrays

Understand the meaning of array index out

of bounds

Become familiar with the restrictions on

array processing


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Chapter Objectives (continued) Discover how to pass an array as a

parameter to a method

Discover how to manipulate data in a two-

dimensional array

Learn about multidimensional arrays


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Array Definition: structured data type with a fixed

number of elements

Elements of an array are also called

components of the array

Every element is of the same type

Elements are accessed using their relative

positions in the array


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One-Dimensional Arrays


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(continued)


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(continued)

intExp = number of components in array >= 0

0


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Array num:int[] num = new int[5];

Arrays


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Array List


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Array List (continued)


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Specifying Array Size During

Program Execution


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The initializer list contains values, called initial

values, that are placed between braces andseparated by commas

Here, sales[0]= 12.25, sales[1]=32.50, sales[2]= 16.90, sales[3]=

23.00, andsal

es

[4]= 45.68

Array Initialization During Declaration


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Array Initialization During Declaration

(continued) When declaring and initializing arrays, the

size of the array is determined by the number

of initial values within the braces If an array is declared and initialized

simultaneously, we do not use the operatornew to instantiate the array object


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Associated with each array that has beeninstantiated, there is a public (final) instancevariable length

The variable length contains the size of the array The variable length can be directly accessed in aprogram using the array name and the dot operator

int[] list = {10, 20, 30, 40, 50, 60};

Arrays and the Instance Variablelength


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Arrays and the Instance Variable

length (continued) This statement creates the array list of six

components and initializes the components

using the values given

Here list.length is 6

int[] numList = new int[10];

This statement creates the array numListof 10 components and initializes eachcomponent to 0


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The value ofnumList.length is 10numList[0] = 5;

numList[1] = 10;

numList[2] = 15;

numList[3] = 20; These statements store 5, 10, 15, and 20, respectively, in

the first four components ofnumList

You can store the number of filled elements, that is, theactual number of elements, in the array in a variable, saynumOfElement

It is a common practice for a program to keep track of thenumber of filled elements in an array

Arrays and the Instance Variablelength (continued)


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Loops used to step through elements in arrayand perform operations

int[] list = new int[100];

int i;

for (i = 0; i < list.length; i++)

//processlist[i], the (i + 1)th

//element of list


list[i] = console.nextInt();


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

Processing One-DimensionalArrays


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Arrays (continued)

Some operations on arrays:

Initialize

Input data

Output stored data

Find largest/smallest/sum/average of elements

double[] sales = new double[10];

int index;

double largestSale, sum, average;


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Code to Initialize Array to

Specific Value (10.00)

for (index = 0; index < sales.length;

index++)sales[index] = 10.00;


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Code to Read Data into Array


index++)sales[index] = console.nextDouble();


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Code to Print Array


index++)System.out.print(sales[index] + " ");


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Code to Find Sum and Average

of Arraysum = 0;


index++)sum = sum + sales[index];

if (sales.length != 0)

average = sum / sales.length;

else

average = 0.0;


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Determining Largest Element in

Array

maxIndex = 0;


index++)

if (sales[maxIndex] < sales[index])

maxIndex = index;

largestSale = sales[maxIndex];


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Array (continued)


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Array (continued)


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Array Index Out of Bounds

Array in bounds if:0


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Declaring Arrays as Formal

Parameters to Methods A general syntax to declare an array as a formal

parameterdataType[] arrayName

public static void arraysAsFormalParameter(int[] listA,

double[] listB, int num){

//...

}

int[] intList = new int[10];

doubl

e[] doubl

eNumLis

t = new doubl

e[15];int number;

arraysAsFormalParameter(intList, doubleNumList,number);


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The Assignment Operators and

Arrays


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The Assignment Operators and

Arrays (continued)


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Relational Operators Arrays

if (listA == listB)...

- The expression listA == listB determines if

the values oflistA and listB are the same and thus

determines whetherlistA and listB refer to the

same array- To determine whetherlistA and listB contain the

same elements, you need to compare them component

by component- You can write a method that returns true if two int

arrays contain the same elements


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Relational Operators and Arrays

(continued)boolean isEqualArrays(int[] firstArray,

int[] secondArray)

{

if (firstArray.length != secondArray.length)

return false;

for (int index = 0; index < firstArray.length;

index++)

if (firstArray[index] != secondArray[index])

return false;

return true;

}

if (isEqualArrays(listA, listB))

...


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Arrays as Parameter Methods


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Methods for Array Processing


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(continued)


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(continued)


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(continued)


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Parallel Arrays Arrays are parallel if corresponding

components hold related information


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Arrays of Objects

Can use arrays to manipulate objects Example: create array named array1 with N

objects of type T

T[] array1 = new T[N] Can instantiate array1 as follows:

for(int j=0; j


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Array ofString Objects

String[] nameList = new String[5];

nameList[0] = "Amanda Green";

nameLi

st[1] = "Vij

ay Aror

a";

nameList[2] = "Sheila Mann";

nameList[3] = "Rohit Sharma";

nameList[4] = "Mandy Johnson";


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Array ofString Objects

(continued)


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Clock[] arrivalTimeEmp = new Clock[100];

Arrays of Objects (continued)


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Instantiating Array Objectsfor (int j = 0; j < arrivalTimeEmp.length; j++)

arri

valTimeEmp[j] = new

Clock();


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arrivalTimeEmp[49].setTime(8, 5, 10);

Instantiating Array Objects (continued)


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Arrays and Variable Length

Parameter List The syntax to declare a variable length formal

parameter (list) is:

dataType ... identifier

A d V i bl L th


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Parameter List (continued)


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A d V i bl L h


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A method can have both a variable length formal

parameter and other formal parameters; consider the

following method heading:public static void myMethod(String

name, double num, int ... intList)

The formal parameter name is of type String, the

formal parameternum is of type double, and the

formal parameterintList

is of variable length The actual parameter corresponding to intList can

be an int array or any number ofint variables and/or

int values


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Parameter List (continued) A method can have at most one variable

length formal parameter

If a method has both a variable lengthformal parameter and other types of formal

parameters, then the variable length formal

parameter must be the last formal parameterof the formal parameter list


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foreach loop

The syntax to use this for loop to process theelements of an array is:

for (dataType identifier : arrayName)

statements

identifier is a variable and the data type ofidentifier is the same as the data type of the array

components


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foreach loop (continued)

sum = 0;for (double num : list)

sum = sum + num;

The for statement in Line 2 is read: for each num in list

The identifiernum is initialized to list[0 In the next iteration, the value ofnum is list[1], and so

on

for (double num : numList)

{if (max < num)

max = num;

}


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Two-Dimensional Arrays


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(continued)

T Di i l A


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double[][] sales = new double[10][5];


(continued)


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intExp1, intExp2 >= 0

indexExp1 = row position

indexExp2 = column position

Accessing Array Elements

A i A El


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Accessing Array Elements

(continued)


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This statement declares and instantiates a two-

dimensional array matrix of 20 rows and 15

columns The value of the expression:

matrix.lengthis 20, the number of rows

Two-Dimensional Arrays and the

Instance Variable length

i i l A d h


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Two-Dimensional Arrays and theInstance Variable length

(continued) Each row of matrix is a one-dimensional array;matrix[0], in fact, refers to the first row

The value of the expression:matrix[0].length

is 15, the number of columns in the first row

matrix[1].length gives the number ofcolumns in the second row, which in this case is 15,

and so on


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Two-Dimensional Arrays: Special

Cases


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Create columns

Two-Dimensional Arrays: Special

Cases (continued)


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Two-Dimensional Array Initialization

During Declaration


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To initialize a two-dimensional array when it is

declared- The elements of each row are enclosed within

braces and separated by commas

- All rows are enclosed within braces


During Declaration (continued)


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During Declaration (continued)


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(continued) Three ways to process 2-D arrays

Entire array

Particular row of array (row processing)

Particular column of array (column processing)

Processing algorithms similar to processing

algorithms of one-dimensional arrays

T Di i l A


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Two-Dimensional Arrays:

ProcessingInitialization

for (row = 0; row < matrix.length; row++)

for (col = 0; col < matrix[row].length;

col++)

matrix[row][col] = 10;

Printfor (row = 0; row < matrix.length; row++)

{


col++)

System.out.printf("%7d", matrix[row][col]);

System.out.println();

}



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I

nputfor (row = 0; row < matrix.length; row++)for (col = 0; col < matrix[row].length;

col++)

matrix[row][col] = console.nextInt();

Sum by Rowfor (row = 0; row < matrix.length; row++)

{

sum = 0;


col++)

sum = sum + matrix[row][col];

System.out.println("Sum of row " + (row + 1)

+ " = "+ sum);

}


Processing (continued)


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Sum by Columnfor (col = 0; col < matrix[0].length; col++)

{

sum = 0;for (row = 0; row < matrix.length; row++)

sum = sum + matrix[row][col];

System.out.println("Sum of column " + (col + 1)

+ " = " + sum);

}




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Largest Element in Each Row


{largest = matrix[row][0];


col++)

if (largest < matrix[row][col])

la

rges

t = ma

trix[row][col

];System.out.println("The largest element of row "

+ (row + 1) + " = " + largest);

}




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Largest Element in Each Column

for (col = 0; col < matrix[0].length; col++)

{largest = matrix[0][col];


if (largest < matrix[row][col])

largest = matrix[row][col];

System.out.println("The largest element of col "+ (col + 1) + " = " + largest);

}




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Multidimensional Arrays

Can define three-dimensional arrays or n-dimensional

array (n can be any number)

Syntax to declare and instantiate array

dataType[][][] arrayName = new

dataType[intExp1][intExp2][intExpn];

Syntax to access component

arrayName[indexExp1][indexExp2][indexExpn]

intExp1, intExp2, ..., intExpn = positive integers

indexExp1,indexExp2, ..., indexExpn= non-negative integers


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Loops to Process

Multidimensional Arrays

double[][][] carDealers = new double[10][5][7];

for (i = 0; i < 10; i++)

for (j = 0; j < 5; j++)

for (k = 0; k < 7; k++)

carDealers[i][j][k] = 10.00;


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Programming Example:

Text Processing Program: reads given text; outputs the text

as is; prints number of lines and number of

times each letter appears in text Input: file containing text to be processed

Output: file containing text, number of

lines, number of times letter appears in text


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Programming Example Solution:

Text Processing An array of 26 representing the letters in the

alphabet

Three methods copyText

characterCount

writeTotal

Value in appropriate index incrementedusing methods and depending on characterread from text


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Chapter Summary

Arrays

Definition

Uses Different Arrays

One-dimensional

Two-dimensional

Multidimensional (n-dimensional) Arrays of objects

Parallel arrays


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Java Programming: From Problem Analysis to Program Design 3e 77

Chapter Summary (continued)

Declaring arrays

Instantiating arrays

Processing arrays

Entire array

Row processing

Column processing

Common operations and methodsperformed on arrays

Manipulating data in arrays

programming lecture 9

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