chapter 9: arrays j ava p rogramming: from problem analysis to program design, from problem analysis...
TRANSCRIPT
Chapter 9: ArraysChapter 9: Arrays
JJavaava PProgramming:rogramming:
From Problem Analysis to Program From Problem Analysis to Program
Design,Design, Second EditionSecond Edition
Java Programming: From Problem Analysis to Program Design, Second Edition 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.
Java Programming: From Problem Analysis to Program Design, Second Edition 3
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.
Java Programming: From Problem Analysis to Program Design, Second Edition 4
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 Design, Second Edition 5
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 Design, Second Edition 6
int[] num = new int[5];
Array num
Java Programming: From Problem Analysis to Program Design, Second Edition 7
Array list
Java Programming: From Problem Analysis to Program Design, Second Edition 8
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 Design, Second Edition 9
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]= 45.68.
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 Design, Second Edition 10
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 Design, Second Edition 11
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 Design, Second Edition 12
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 Design, Second Edition 13
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 Design, Second Edition 14
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 Design, Second Edition 15
Code to Read Data into Array
for (index = 0; index < sales.length; index++) sales[index] = console.nextDouble();
Java Programming: From Problem Analysis to Program Design, Second Edition 16
Code to Print Array
for (index = 0; index < sales.length; index++) System.out.print(sales[index] + " ");
Java Programming: From Problem Analysis to Program Design, Second Edition 17
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 Design, Second Edition 18
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 Design, Second Edition 19
Determining Largest Element in Array
Java Programming: From Problem Analysis to Program Design, Second Edition 20
Array Index Out of Bounds
An array is in bounds if:
0 <= index <= arraySize – 1
If index < 0 or index > arraySize:
ArrayIndexOutOfBoundsException exception is thrown.
Base address: Memory location of the first component in an array.
Java Programming: From Problem Analysis to Program Design, Second Edition 21
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 Design, Second Edition 22
The Assignment Operators and Arrays
Java Programming: From Problem Analysis to Program Design, Second Edition 23
The Assignment Operators and Arrays
Java Programming: From Problem Analysis to Program Design, Second Edition 24
for (int index = 0; index < listA.length;
index++)
listB[index] = listA[index];
The Assignment Operators and Arrays
Java Programming: From Problem Analysis to Program Design, Second Edition 25
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 Design, Second Edition 26
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 Design, Second Edition 27
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 Design, Second Edition 28
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 Design, Second Edition 29
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 Design, Second Edition 30
Parallel Arrays
Arrays are parallel if the corresponding components hold related information.
Java Programming: From Problem Analysis to Program Design, Second Edition 31
Arrays of Objects
Can use arrays to manipulate objects. Example: Create an 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();
Java Programming: From Problem Analysis to Program Design, Second Edition 32
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";
Java Programming: From Problem Analysis to Program Design, Second Edition 33
Array of String Objects
Java Programming: From Problem Analysis to Program Design, Second Edition 34
Clock[] arrivalTimeEmp = new Clock[100];
Arrays of Objects
Java Programming: From Problem Analysis to Program Design, Second Edition 35
Instantiating Array Objectsfor (int j = 0; j < arrivalTimeEmp.length; j++) arrivalTimeEmp[j] = new Clock();
Java Programming: From Problem Analysis to Program Design, Second Edition 36
arrivalTimeEmp[49].setTime(8, 5, 10);
Instantiating Array Objects
Java Programming: From Problem Analysis to Program Design, Second Edition 37
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 Design, Second Edition 38
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 Design, Second Edition 39
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, 17.89
92.34, 112.0, 77, 11, 22,
86.62);
System.out.println(largest(numberList));
Java Programming: From Problem Analysis to Program Design, Second Edition 40
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 Design, Second Edition 41
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;}
Java Programming: From Problem Analysis to Program Design, Second Edition 42
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 = newdataType[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 Design, Second Edition 43
Two-Dimensional Arrays
Can specify different number of columns for each row (ragged 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 Design, Second Edition 44
double[][]sales = new double[10][5];
Two-Dimensional Arrays
Java Programming: From Problem Analysis to Program Design, Second Edition 45
Accessing Two-Dimensional Array Components
Java Programming: From Problem Analysis to Program Design, Second Edition 46
Two-Dimensional Arrays: Special Cases
Java Programming: From Problem Analysis to Program Design, Second Edition 47
Two-Dimensional Arrays: Processing
Initialization
for (row = 0; row < matrix.length; row++) for (col = 0; col < matrix[row].length; col++) matrix[row][col] = 10;
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 Design, Second Edition 48
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 Design, Second Edition 49
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 Design, Second Edition 50
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 Design, Second Edition 51
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 Design, Second Edition 52
Multidimensional Arrays
Can define three-dimensional arrays or n-dimensional arrays (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
Java Programming: From Problem Analysis to Program Design, Second Edition 53
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;
Java Programming: From Problem Analysis to Program Design, Second Edition 54
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 each letter appears in text.
Java Programming: From Problem Analysis to Program Design, Second Edition 55
Programming Example Solution: Text Processing
An array of 26 representing the letters in the alphabet. Three methods:
copyText characterCount writeTotal
Value in appropriate index is incremented using methods and depends on character read from text.
Java Programming: From Problem Analysis to Program Design, Second Edition 56
Chapter Summary Arrays
Definition Uses
Different arrays One-dimensional Two-dimensional Multidimensional (n-dimensional) Arrays of objects Parallel arrays
Java Programming: From Problem Analysis to Program Design, Second Edition 57
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