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Chapter 9: Arrays. J ava P rogramming: From Problem Analysis to Program Design, Second Edition. Chapter Objectives. Learn about arrays. Explore how to declare and manipulate data into arrays. Understand the meaning of “array index out of bounds.”

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Chapter 9 arrays

Chapter 9: Arrays

JavaProgramming:

From Problem Analysis to Program Design,

Second Edition


Chapter objectives
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


Chapter objectives1
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


Array
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


One dimensional arrays
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


Int num new int 5

Array num

int[] num = new int[5];

Java Programming: From Problem Analysis to Program Design, Second Edition


Array list
Array list

Java Programming: From Problem Analysis to Program Design, Second Edition


Specifying Array Size During Program Execution

int arraySize;

System.out.print("Enter the size of "

+ "the array: ");

arraySize = console.nextInt();

System.out.println();

int[] list = new int[arraySize];

Java Programming: From Problem Analysis to Program Design, Second Edition


Array Initialization During Declaration

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.

Java Programming: From Problem Analysis to Program Design, Second Edition


Arrays and the Instance Variable length

  • 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};

Java Programming: From Problem Analysis to Program Design, Second Edition


Arrays and the Instance Variable length

  • 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.

Java Programming: From Problem Analysis to Program Design, Second Edition


Processing One-Dimensional Arrays

  • 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] + " ");

Java Programming: From Problem Analysis to Program Design, Second Edition


Arrays
Arrays

  • Some operations on arrays:

    • Initialize

    • Input data

    • Output stored data

    • Find largest/smallest/sum/average of elements

double[] sales = newdouble[10];

int index;

double largestSale, sum, average;

Java Programming: From Problem Analysis to Program Design, Second Edition


Code to initialize array to specific value 10 00
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


Code to read data into array
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


Code to print array
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


Code to find sum and average of array
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


Determining largest element in array
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


Determining largest element in array1
Determining Largest Element in Array

Java Programming: From Problem Analysis to Program Design, Second Edition


Array index out of bounds
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


Declaring arrays as formal parameters to methods
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 = newint[10];

double[] doubleNumList = newdouble[15];

int number;

arraysAsFormalParameter(intList, doubleNumList, number);

Java Programming: From Problem Analysis to Program Design, Second Edition


The assignment operators and arrays
The Assignment Operators and Arrays

Java Programming: From Problem Analysis to Program Design, Second Edition


The assignment operators and arrays1
The Assignment Operators and Arrays

Java Programming: From Problem Analysis to Program Design, Second Edition


The Assignment Operators and Arrays

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

index++)

listB[index] = listA[index];

Java Programming: From Problem Analysis to Program Design, Second Edition


Relational operators arrays
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


Relational operators and arrays
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


Methods for array processing
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


Methods for Array Processing

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;

}

Java Programming: From Problem Analysis to Program Design, Second Edition


Methods for Array Processing

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];

}

Java Programming: From Problem Analysis to Program Design, Second Edition


Parallel arrays
Parallel Arrays

  • Arrays are parallel if the corresponding components hold related information.

Java Programming: From Problem Analysis to Program Design, Second Edition


Arrays of objects
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


Array of string objects
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


Array of string objects1
Array of String Objects

Java Programming: From Problem Analysis to Program Design, Second Edition


Clock arrivaltimeemp new clock 100

Arrays of Objects

Clock[] arrivalTimeEmp = new Clock[100];

Java Programming: From Problem Analysis to Program Design, Second Edition


Instantiating array objects
Instantiating Array Objects

for (int j = 0; j < arrivalTimeEmp.length; j++)

arrivalTimeEmp[j] = new Clock();

Java Programming: From Problem Analysis to Program Design, Second Edition


Instantiating Array Objects

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

Java Programming: From Problem Analysis to Program Design, Second Edition


Arrays and variable length parameter list
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


Arrays and variable length parameter list1
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


Arrays and variable length parameter list2
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


Foreach loop
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


Foreach loop1
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


Two dimensional arrays
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


Two dimensional arrays1
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


Double sales new double 10 5

Two-Dimensional Arrays

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

Java Programming: From Problem Analysis to Program Design, Second Edition


Accessing two dimensional array components
Accessing Two-Dimensional Array Components

Java Programming: From Problem Analysis to Program Design, Second Edition


Two dimensional arrays special cases
Two-Dimensional Arrays: Special Cases

Java Programming: From Problem Analysis to Program Design, Second Edition


Two dimensional arrays processing
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 Design, Second Edition


Two dimensional arrays processing1
Two-Dimensional Arrays: Processing

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);

}

Java Programming: From Problem Analysis to Program Design, Second Edition


Two dimensional arrays processing2
Two-Dimensional Arrays: Processing

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);

}

Java Programming: From Problem Analysis to Program Design, Second Edition


Two dimensional arrays processing3
Two-Dimensional Arrays: Processing

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);

}

Java Programming: From Problem Analysis to Program Design, Second Edition


Two dimensional arrays processing4
Two-Dimensional Arrays: Processing

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);

}

Java Programming: From Problem Analysis to Program Design, Second Edition


Multidimensional arrays
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


Loops to process multidimensional arrays
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


Programming example text processing
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


Programming example solution text processing
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


Chapter summary
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


Chapter summary1
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

Java Programming: From Problem Analysis to Program Design, Second Edition


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