Chapter 9: Arrays J ava P rogramming: From Problem Analysis to Program Design, From Problem Analysis to Program Design,

Java Programming: From Problem Analysis to Program Design2 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.

Java Programming: From Problem Analysis to Program Design3 Chapter Objectives  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.

4 Motivation Write a program to read 5 numbers, find their sum and print them in reverse order. import java.util.*; public class RevOrder{ static Scanner console = new Scanner(System.in); public static void main(String[] args){ int item0, item1, item2, item3, item4; int sum; System.out.println("Enter 5 numbers: "); item0=console.nextInt(); item1=console.nextInt(); item2=console.nextInt(); item3=console.nextInt(); item4=console.nextInt(); sum = item0+item1+item2+item3+item4; System.out.println("Sum = " + sum); System.out.print("Numbers is reverse = "); System.out.println(item4+" "+item3+" "+item2+" "+item1+" "+item0); } } Enter 5 numbers: Sum = 26 Numbers is reverse =

Java Programming: From Problem Analysis to Program Design5 Array  A structured data type with a fixed number of components.  Every component is of the same type.  Components are accessed using their relative positions in the array.

Java Programming: From Problem Analysis to Program Design6 One-Dimensional Arrays  Syntax to instantiate an array:  dataType[ ] arrayName; arrayName = new dataType[intExp]  dataType[ ] arrayName = new dataType[intExp]  dataType[ ] arrayName1, arrayName2;  Syntax to access an array component:  arrayName[indexExp]  intExp = number of components in array >= 0  0 <= indexExp < intExp

Java Programming: From Problem Analysis to Program Design7 int[] num = new int[5]; Array num

Java Programming: From Problem Analysis to Program Design8 Array list

Java Programming: From Problem Analysis to Program Design9 int arraySize; System.out.print("Enter the size of " + "the array: "); arraySize = console.nextInt(); System.out.println(); int[] list = new int[arraySize]; Specifying Array Size During Program Execution

Java Programming: From Problem Analysis to Program Design10 double[] sales = {12.25, 32.50, 16.90, 23, 45.68};  The values, called initial values, are placed between braces and separated by commas.  Here, sales[0]= 12.25, sales[1]= 32.50, sales[2]= 16.90, sales[3]= 23.00, and sales[4]=  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. Array Initialization During Declaration

Java Programming: From Problem Analysis to Program Design11  A public instance variable length is associated with each array that has been instantiated.  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.  This statement creates the array list of six components and initializes the components using the values given. Here list.length is 6. int[] list = {10, 20, 30, 40, 50, 60}; Arrays and the Instance Variable length

Java Programming: From Problem Analysis to Program Design12  This statement creates the array numList of 10 components and initializes each component to 0. int[] numList = new int[10];  The value of numList.length is 10.  These statements store 5, 10, 15, and 20, respectively, in the first four components of numList. numList[0] = 5; numList[1] = 10; numList[2] = 15; numList[3] = 20;  You can store the number of filled elements, that is, the actual number of elements, in the array in a variable, say noOfElement. 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

Java Programming: From Problem Analysis to Program Design13  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

Java Programming: From Problem Analysis to Program Design14 Arrays  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;

Java Programming: From Problem Analysis to Program Design15 Code to Initialize Array to Specific Value (10.00) for (index = 0; index < sales.length; index++) sales[index] = 10.00;

Java Programming: From Problem Analysis to Program Design16 Code to Read Data into Array for (index = 0; index < sales.length; index++) sales[index] = console.nextDouble();

Java Programming: From Problem Analysis to Program Design17 Code to Print Array for (index = 0; index < sales.length; index++) System.out.print(sales[index] + " ");

Java Programming: From Problem Analysis to Program Design18 Code to Find Sum and Average of Array sum = 0; for (index = 0; index < sales.length; index++) sum = sum + sales[index]; if (sales.length != 0) average = sum / sales.length; else average = 0.0;

Java Programming: From Problem Analysis to Program Design19 Determining Largest Element in Array maxIndex = 0; for (index = 1; index < sales.length; index++) if (sales[maxIndex] < sales[index]) maxIndex = index; largestSale = sales[maxIndex];

Java Programming: From Problem Analysis to Program Design20 Determining Largest Element in Array

//Program to read five numbers, find their sum, and //print the numbers in the reverse order. import java.util.*; public class ReversePrintII { static Scanner console = new Scanner(System.in); public static void main(String[] args) { int[] items = new int[5]; //declare an array item of //five elements int sum; System.out.println("Enter five integers:"); sum = 0; for (int counter = 0; counter < items.length; counter++) { items[counter] = console.nextInt(); sum = sum + items[counter]; } System.out.println("The sum of the numbers = “+ sum); Java Programming: From Problem Analysis to Program Design21

System.out.print("The numbers in the reverse " + "order are: "); //print the numbers in the reverse order for (int counter = items.length - 1; counter >= 0; counter--) System.out.print(items[counter] + " "); System.out.println(); } } Java Programming: From Problem Analysis to Program Design22

Java Programming: From Problem Analysis to Program Design23 Array Index Out of Bounds  An array is in bounds if: 0 <= index <= arraySize – 1  If index arraySize : ArrayIndexOutOfBoundsException exception is thrown.  Base address: Memory location of the first component in an array.  Base address of list is the address of list[0].

Java Programming: From Problem Analysis to Program Design24 Declaring Arrays as Formal Parameters to Methods 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);

Java Programming: From Problem Analysis to Program Design25 The Assignment Operators and Arrays

Java Programming: From Problem Analysis to Program Design26 The Assignment Operators and Arrays

Java Programming: From Problem Analysis to Program Design27 for (int index = 0; index < listA.length; index++) listB[index] = listA[index]; The Assignment Operators and Arrays

Java Programming: From Problem Analysis to Program Design28 Relational Operators Arrays if (listA == listB)...  The expression listA == listB determines if the values of listA and listB are the same, thus determining 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.

Java Programming: From Problem Analysis to Program Design29 Relational Operators and Arrays 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))...

Java Programming: From Problem Analysis to Program Design30 Methods for Array Processing public static void fillArray(int[] list, int noOfElements) { int index; for (index = 0; index < noOfElements; index++) list[index] = console.nextInt(); }

Java Programming: From Problem Analysis to Program Design31 public static void printArray(int[] list, int noOfElements) { int index; for (index = 0; index < noOfElements; index++) System.out.print(list[index] + " "); } public static int sumArray(int[] list, int noOfElements) { int index; int sum = 0; for (index = 0; index < noOfElements; index++) sum = sum + list[index]; return sum; } Methods for Array Processing

Java Programming: From Problem Analysis to Program Design32 public static int indexLargestElement(int[] list, int noOfElements) { int index; int maxIndex = 0; for (index = 1; index < noOfElements; index++) if (list[maxIndex] < list[index]) maxIndex = index; return maxIndex; } public static void copyArray(int[] list1, int[] list2, int noOfElements) { int index; for (index = 0; index < noOfElements; index++) list2[index] = list1[index]; } Methods for Array Processing

Java Programming: From Problem Analysis to Program Design33 Parallel Arrays  Arrays are parallel if the corresponding components hold related information. int [] studentId = new int[50]; char[] courseGrade = new char[50]; studentId[3] and courseGrade[3] holds the data for the same student. studentId courseGrade 2345 A 4563 C 4590 C 2404 B

Java Programming: From Problem Analysis to Program Design34 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";  You can use String methods to work with the objects of nameList. nameList[0].equals(“Amanda Green”) // true nameList[4].substring(0,5) //Mandy

Java Programming: From Problem Analysis to Program Design35 Array of String Objects

Java Programming: From Problem Analysis to Program Design36 Arrays and Variable Length Parameter List  The syntax to declare a variable length formal parameter (list) is: dataType... identifier

Java Programming: From Problem Analysis to Program Design37 Arrays and Variable Length Parameter List public static double largest(double... numList) { double max; int index; if (numList.length != 0) { max = list[0]; for (index = 1; index < numList.length; index++) { if (max < numList [index]) max = numList [index]; } return max; } return 0.0; }

Java Programming: From Problem Analysis to Program Design38 Arrays and Variable Length Parameter List double num1 = largest(34, 56); double num2 = largest(12.56, 84, 92); double num3 = largest(98.32, 77, 64.67, 56); System.out.println(largest(22.50, 67.78, 92.58, 45, 34, 56)); double[] numberList = {18. 50, 44, 56.23, , 112.0, 77, 11, 22, 86.62); System.out.println(largest(numberList));

39 Rules to follow when using a variable length formal parameter list: 1.A method can have both a variable length formal parameter and other formal parameter. public static void myMethod (String name, double num, int … intList) 2.A method can have at most one variable length formal parameter. 3.If a method has both a variable length formal parameter and other formal parameter, then the variable length formal parameter must be the last). Arrays and Variable Length Parameter List

Java Programming: From Problem Analysis to Program Design40 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.

Java Programming: From Problem Analysis to Program Design41 foreach loop 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 on. for (double num : numList) { if (max < num) max = num; }

42 [Red][Brown][Black][White][Gray] [GM] [Ford]63664 [Toyota]35367 [BMW]82753 [Nissan] [Volvo]15797 Two-Dimensional Arrays inStock

Java Programming: From Problem Analysis to Program Design43 Two-Dimensional Arrays  Data is sometimes in table form (difficult to represent using a one-dimensional array).  To declare/instantiate a two-dimensional array: dataType[ ][ ] arrayName = new dataType[intExp1][intExp2];  To access a component of a two-dimensional array: arrayName[indexExp1][indexExp2];  intExp1, intExp2 >= 0  indexExp1 = row position  indexExp2 = column position

Java Programming: From Problem Analysis to Program Design44 double[][]sales = new double[10][5]; Two-Dimensional Arrays

Java Programming: From Problem Analysis to Program Design45 Accessing Two-Dimensional Array Components

46 int [][] matrix = new int[20][15]; 20 rows 15 columns matrix.length = 20 //number of rows  Each row of matrix is 1-D array matrix.[0].length = 15 //# of columns in 1 st row matrix.[1].length = 15 // # of columns in 2 nd row Two-Dimensional Arrays

47 Two-Dimensional Arrays: Special Cases  Can specify different number of columns for each row (ragged arrays). In this case, each row must be instantiated separately.

48 Two-Dimensional Arrays: Special Cases To create this array, first we create 1-D array board of 5 rows: int[] board = new int[5]; board[0] = new int[6]; board[1] = new int[2]; board[2] = new int[2]; board[3] = new int[3]; board[4] = new int[4];

49 Two Dimensional Array Initialization During Declaration int[][] board = {{2,3,1}, {15,25,13}, {20, 4, 7}}; [0][1][2] [0]231 [1] [2]2047 board What is the array created after this statement: int[][] table = {{2,3,1,5}, {15,25}, {4, 23, 45}};

Java Programming: From Problem Analysis to Program Design50 Two-Dimensional Arrays  Three ways to process two-dimensional arrays:  Entire array.  Particular row of array (row processing).  Particular column of array (column processing).  Processing algorithms is similar to processing algorithms of one-dimensional arrays.

Java Programming: From Problem Analysis to Program Design51 Two-Dimensional Arrays: Processing Initialization for (row = 0; row < matrix.length; row++) for (col = 0; col < matrix[row].length; col++) matrix[row][col] = 10; Print for (row = 0; row < matrix.length; row++) { for (col = 0; col < matrix[row].length; col++) System.out.printf("%7d", matrix[row][col]); System.out.println(); }

Java Programming: From Problem Analysis to Program Design52 Input for (row = 0; row < matrix.length; row++) for (col = 0; col < matrix[row].length; col++) matrix[row][col] = console.nextInt(); Sum by Row for (row = 0; row < matrix.length; row++) { sum = 0; for (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

Java Programming: From Problem Analysis to Program Design53 Sum by Column for (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); } Two-Dimensional Arrays: Processing

Java Programming: From Problem Analysis to Program Design54 Largest Element in Each Row for (row = 0; row < matrix.length; row++) { largest = matrix[row][0]; for (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); } Two-Dimensional Arrays: Processing

Java Programming: From Problem Analysis to Program Design55 Largest Element in Each Column for (col = 0; col < matrix[0].length; col++) { largest = matrix[0][col]; for (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); } Two-Dimensional Arrays: Processing

Java Programming: From Problem Analysis to Program Design56 Multidimensional Arrays  Can define three-dimensional arrays or n-dimensional arrays (n can be any number).  Syntax to declare and instantiate array: d ataType[][]…[] 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

Java Programming: From Problem Analysis to Program Design57 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;

Code Detection // This program checks whether the message received at the destination // is error-free. If there is an error in the message, then the // program outputs an error message and asks for retransmission. import java.util.*; public class CodeDetection { static Scanner console = new Scanner(System.in); public static void main(String[] args) { int codeLength; //Step 1 System.out.print("Enter the length of " + " the code: "); //Step 2 codeLength = console.nextInt(); //Step 3 System.out.println(); int[] codeArray = new int[codeLength]; //Step 4 readCode(codeArray); //Step 5 compareCode(codeArray); //Step 6 } Java Programming: From Problem Analysis to Program Design58

public static void readCode(int[] list) { System.out.print("Enter the secret code: "); for (int count = 0; count < list.length; count++) list[count] = console.nextInt(); System.out.println(); } Java Programming: From Problem Analysis to Program Design59

public static void compareCode(int[] list) { //Step a: Declare the variables int length2; int digit; boolean codeOk; int count; codeOk = true; //Step b System.out.println("Enter the length of the copy of " + "the secret code \nand a copy of " + "the secret code: "); length2 = console.nextInt(); //Step c if (list.length != length2) //Step d { System.out.println("The original code and " + "its copy are not of " + "the same length."); return; } System.out.println("Code Digit Code Digit " + "Copy"); //Step e Java Programming: From Problem Analysis to Program Design60

for (count = 0; count < list.length; count++) //Step f { digit = console.nextInt(); //Step f.1 System.out.printf("%5d %15d", list[count], digit); //Step f.2 if (digit != list[count]) //Step f.3 { System.out.println(" corresponding code " + "digits not the same"); codeOk = false; } else System.out.println(); } if (codeOk) //Step g System.out.println("Message transmitted OK."); else System.out.println("Error in transmission. " + "Retransmit!!"); } } Java Programming: From Problem Analysis to Program Design61

Java Programming: From Problem Analysis to Program Design62 Chapter Summary  Arrays  Definition  Uses  Different arrays  One-dimensional  Two-dimensional  Multidimensional (n-dimensional)  Parallel arrays

Java Programming: From Problem Analysis to Program Design63 Chapter Summary  Declaring arrays  Instantiating arrays  Processing arrays  Entire array  Row processing  Column processing  Common operations and methods performed on arrays  Manipulating data in arrays