9781439035665 ppt ch09

Java Programming: From Problem Analysis to Program Design, 4e

Chapter 9Arrays

Java Programming: From Problem Analysis to Program Design, 4e 2

Chapter Objectives

• Learn about arrays

• Explore how to declare and manipulate data into arrays

• Understand the meaning of “array index out of bounds”

• Become familiar with the restrictions on array processing


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


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


One-Dimensional Arrays


One-Dimensional Arrays (continued)


One-Dimensional Arrays (continued)

•intExp = number of components in array >= 0•0 <= indexExp <= intExp


• Array num:int[] num = new int[5];

Arrays


• Array num:int[] num = new int[5];

Arrays (continued)


Array List


Array List (continued)


Specifying Array Size During Program Execution


• The initializer list contains values, called initial values, that are placed between braces and separated by commas

•sales[0]= 12.25, sales[1]= 32.50, sales[2]= 16.90, sales[3]= 23.00, and sales[4]= 45.68

Array Initialization During Declaration


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 operator new to instantiate the array object


• Associated with each array that has been instantiated, there is a public (final) instance variable length

• The variable length contains the size of the array • The variable length can be directly accessed in a

program using the array name and the dot operator

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

Arrays and the Instance Variable length


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 numList of 10 components and initializes each component to 0


• The value of numList.length is 10 numList[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 of numList

• You can store the number of filled elements, that is, the actual number of elements, in the array in a variable, say numOfElement

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

Arrays and the Instance Variable length (continued)


• Loops used to step through elements in array and perform operations

int[] list = new int[100];int i;

for (i = 0; i < list.length; i++) //process list[i], the (i + 1)th //element of list

for (i = 0; i < list.length; i++) list[i] = console.nextInt();

for (i = 0; i < list.length; i++) System.out.print(list[i] + " ");

Processing One-Dimensional Arrays


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;


Code to Initialize Array to Specific Value (10.00)

for (int index = 0; index < sales.length; index++) sales[index] = 10.00;


Code to Read Data into Array

for (int index = 0; index < sales.length; index++) sales[index] = console.nextDouble();


Code to Print Array

for (int index = 0; index < sales.length; index++) System.out.print(sales[index] + " ");


Code to Find Sum and Average of Array

sum = 0;for (int index = 0; index < sales.length; index++) sum = sum + sales[index];

if (sales.length != 0) average = sum / sales.length;else average = 0.0;


Determining Largest Element in Array

maxIndex = 0;

for (int index = 1; index < sales.length; index++) if (sales[maxIndex] < sales[index]) maxIndex = index;

largestSale = sales[maxIndex];


Determining Largest Element in Array (continued)


Array Index Out of Bounds

• Array in bounds if:0 <= index <= arraySize – 1

• If index < 0 or index > arraySize:

ArrayIndexOutOfBoundsException exception is thrown

• Base address: memory location of first component in array


Declaring Arrays as Formal Parameters to Methods

• A general syntax to declare an array as a formal parameter dataType[] arrayName

public static void arraysAsFormalParameter(int[] listA, double[] listB, int num){ //...}int[] intList = new int[10];double[] doubleNumList = new double[15];int number;

arraysAsFormalParameter(intList, doubleNumList, number);


The Assignment Operators and Arrays


The Assignment Operators and Arrays (continued)


Relational Operators and Arrays

• if (listA == listB)...- The expression listA == listB determines if the values of listA and listB are the same and thus determines whether listA and listB refer to the same array- To determine whether listA 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


Relational Operators and Arrays (continued)

boolean areEqualArrays(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 (areEqualArrays(listA, listB))...


Arrays as Parameter Methods


Methods for Array Processing


Methods for Array Processing (continued)


• Suppose that you want to determine whether 27 is in the list; • First you compare 27 with list[0]• Because list[0] ≠ 27, you then compare 27 with list[1]

• Because list[1] ≠ 27, you compare 27 with list[2]; Because list[2] = 27, the search stops

• This search is successful


• Search for 10• Search starts at the first element in the list, that is, at list[0]

• This time, the search item, which is 10, is compared with every item in the list; eventually, no more data is left in the list to compare with the search item; this is an unsuccessful search


public static int seqSearch(int[] list, int listLength, int searchItem){ int loc; boolean found = false; loc = 0; while (loc < listLength && !found) if (list[loc] == searchItem) found = true; else loc++;

if (found) return loc; else return -1;}


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 <array1.length; j++)

array1[j] = new T();


Array of String Objects

String[] nameList = new String[5];

nameList[0] = "Amanda Green";

nameList[1] = "Vijay Arora";

nameList[2] = "Sheila Mann";

nameList[3] = "Rohit Sharma";

nameList[4] = "Mandy Johnson";


Array of String Objects (continued)


Clock[] arrivalTimeEmp = new Clock[100]; Arrays of Objects (continued)


Instantiating Array Objectsfor (int j = 0; j < arrivalTimeEmp.length; j++) arrivalTimeEmp[j] = new Clock();


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

Instantiating Array Objects (continued)


Arrays and Variable Length Parameter List

• The syntax to declare a variable length formal parameter (list) is:

dataType ... identifier


Arrays and Variable Length Parameter List (continued)



• 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 parameter num is of type double, and the formal parameter intList is of variable length

• The actual parameter corresponding to intList can be an int array or any number of int variables and/or int values



• A method can have at most one variable length formal parameter

• If a method has both a variable length formal parameter and other types of formal parameters, then the variable length formal parameter must be the last formal parameter of the formal parameter list


foreach Loop

• The syntax to use this for loop to process the elements of an array is:

for (dataType identifier : arrayName) statements

•identifier is a variable, and the data type of identifier is the same as the data type of the array components


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 identifier num is initialized to list[0]• In the next iteration, the value of num is list[1], and so

onfor (double num : numList){ if (max < num) max = num;}


Two-Dimensional Arrays


Two-Dimensional Arrays (continued)


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



• intExp1, intExp2 >= 0• indexExp1 = row position• indexExp2 = column position

Accessing Array Elements


Accessing Array Elements (continued)


• This statement declares and instantiates a two-dimensional array matrix of 20 rows and 15 columns

• The value of the expression:matrix.length is 20, the number of rows

Two-Dimensional Arrays and the Instance Variable length


Two-Dimensional Arrays and the Instance 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].lengthis 15, the number of columns in the first row

• matrix[1].length gives the number of columns in the second row, which in this case is 15, and so on


Two-Dimensional Arrays: Special Cases


•Create columns

Two-Dimensional Arrays: Special Cases (continued)


Two-Dimensional Array Initialization During Declaration


• 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

Two-Dimensional Array Initialization During Declaration (continued)


Two-Dimensional Array Initialization During Declaration

(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


Two-Dimensional Arrays: Processing

Initialization

for (int row = 0; row < matrix.length; row++) for (int col = 0; col < matrix[row].length; col++) matrix[row][col] = 10;Printfor (int row = 0; row < matrix.length; row++){ for (int col = 0; col < matrix[row].length; col++) System.out.printf("%7d", matrix[row][col]); System.out.println();}


Inputfor (int row = 0; row < matrix.length; row++) for (int col = 0; col < matrix[row].length; col++) matrix[row][col] = console.nextInt();

Sum by Rowfor (int row = 0; row < matrix.length; row++){ sum = 0; for (int col = 0; col < matrix[row].length; col++) sum = sum + matrix[row][col]; System.out.println("Sum of row " + (row + 1) + " = "+ sum);}

Two-Dimensional Arrays: Processing (continued)


Sum by Column for (int col = 0; col < matrix[0].length; col++){ sum = 0; for (int row = 0; row < matrix.length; row++) sum = sum + matrix[row][col]; System.out.println("Sum of column " + (col + 1) + " = " + sum);}



Largest Element in Each Row

for (int row = 0; row < matrix.length; row++){ largest = matrix[row][0]; for (int col = 1; col < matrix[row].length; col++) if (largest < matrix[row][col]) largest = matrix[row][col]; System.out.println("The largest element of row " + (row + 1) + " = " + largest);}



Largest Element in Each Column

for (int col = 0; col < matrix[0].length; col++){ largest = matrix[0][col]; for (int row = 1; row < matrix.length; row++) if (largest < matrix[row][col]) largest = matrix[row][col]; System.out.println("The largest element of col " + (col + 1) + " = " + largest);}



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


Loops to Process Multidimensional Arrays

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

for (int i = 0; i < 10; i++) for (int j = 0; j < 5; j++) for (int k = 0; k < 7; k++) carDealers[i][j][k] = 10.00;


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


Programming Example Solution: Text Processing

• An array of 26 representing the letters in the alphabet

• Three methods– copyText – characterCount – writeTotal

• Value in appropriate index incremented using methods and depending on character read from text


Chapter Summary

• Arrays– Definition– Uses

• Different Arrays– One-dimensional– Two-dimensional– Multidimensional (n-dimensional)– Arrays of objects– Parallel arrays


Chapter Summary (continued)

• Declaring arrays• Instantiating arrays• Processing arrays

– Entire array– Row processing– Column processing

• Common operations and methods performed on arrays

• Manipulating data in arrays

9781439035665 ppt ch09

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