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ARRAY

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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.

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.

Chapter Objectives

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Why do need array

Let consider the following problem

How do we write Java program that read five

numbers, find the sum, and prints the numbers

in reverse order

Normally, we need to store all the numbers in 5

variables before we can print it in reverse order

Let see the following code. (next slide).

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import java.util.*;

public class ReverseOrder

{

public static void main(String [] args)

{

int item0, item1, item2, item3, item4;

int sum;Scanner input = new Scanner(System.in);

System.out.println("Enter five integers one number per line");

item0 = input.nextInt();


item2 = input.nextInt();item3 = input.nextInt();


sum = item0 + item1 + item2 + item3 + item4;

System.out.println("The sum of the numbers = " + sum);

System.out.println("The numbers in reverse order are: ");

System.out.println(item4 + " " + item3 + " " + item2 + " " + item1 +" " + item0);

}

}

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We need 5 variables to hold the data

What happen if we want to read 100 (or more)

numbers and print them in reverse order.

So, we need 100 variables to hold all data.(item0, item1, item2, item3, item4, item5,100)

For large of data, this code is not desirable.

We need an ARRAY.

continue

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What is Array

A structured data type with a fixed number of

components.

Every component is of the same type.

Components are accessed using their relativepositions in the array.

Types of array

- One-Dimensional array

- Two-Dimensional array

- Multi Dimensional array

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One-Dimensional Arrays

Syntax to declare an array:

[] = new [intExp];

Or

[]= new [intExp];

1. dataType : a type of data will be store in

array or component type

2. arrayName : a reference variable for array

3. intExp : size of an array (> 0)

Syntax to access an array component:

- arrayName[indexExp]

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Example

int[] num = new int[5]; or

int num[] = new int[5];

This statement declare and

creates the arraynumof 5

components.

Each component is intdata type

The components are num[0],

num[1], num[2], num[3], num[4]

The value in square bracket [ ] is

call index and it start at 0

num

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continue

element

index

In java, [ ] is call as array subscripting operator

Items in an array is called elements

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Continue

Array of five

integers called test

Array of five

characters

called grade

test[0] = 85;

test[1] = 98;

test[2] = 75;

test[3] = 87;

test[4] = 68;

grade[0] = B;

grade[1] = C;

grade[2] = B;

grade[3] = A;

grade[4] = C;

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Assign a value into array

int[] list = new int[10];

Assume the declaration as above.

Statement;

list[3] = 10;

list[6] = 35;

list[5] = list[3] + list[6];

will store 10, 45 and 35 into the array in list[3],

list[5] and list[6] respectively. (see next figure)

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Specifying Array Size During Program

Execution (dynamic array)

Array that are created during program executionis called dynamic array

Enables user to specify the size of the array

int arraySize;

System.out.print("Enter the size of the array: ");arraySize = input.nextInt();

int[] list = new int[arraySize];

The system use the value ofarraysize to instantiate

the object list

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Array Initialization During Declaration

We also can assign a value into the array during declarationdouble[]sales = {12.25, 32.50, 16.90, 23.00,

45.68};

The values, called initial values, are placedbetween braces and separated by commas

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.

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Arrays and the Instance Variable length

A public instance variable lengthis associatedwith 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.

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

This statement creates the array list of sixcomponents and initializes the components using the

values given.

Here list.length is 6.

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Loops and Arrays

Loops can be used to process array in severalways:

1. Initialing an array to a specific value

2. Input data into an array

3. Printing an array

4. Find the sum and average of an array

5. Determine the largest element in the array

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1. Initializing an array to a specific value

eg.to initialize every component of the array sale with a

value of 10.00

double[] sales = new double[10];

int index;

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

sales[index] = 10.00;

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2. Input data into an array


int index;

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

sales[index] = input.nextDouble();

3. Printing an array


int index;

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

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

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4. Find the sum and average of an array


int index, sum;double average;

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;

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5. Determining the largest element in the array


int index, maxIndex;

double largestSale;

maxIndex = 0;

for(index = 1; index

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continue

Suppose the array salesis as figure 9.5

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Array Index Out of Bounds

An array is in bounds if:

0

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example

Consider the following declaration:

double[] num = double[10];

int i;

The component num[i] is valid if i = 0, 1, 2.9

When i < 0 or i >= 10, the component num[i] is

invalid (the index is out of bounds)

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Consider the following loopsfor (i = 0; i

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Manipulate data into arrays

Searching a value

Calculation

Reverse element

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Searching a value

Eg.- A method to search an array of integer The Search method return the location of

the first array element equal to the search value

searchValue = 60;

int[] num = {10,20,30,40,50,60,70,80,90,100};

int location;

for (int i=0; i < num.length; i++)

if(num[i] = = searchValue)

location = i;

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Assume the num values as below:

int[] num = {10,20,30,40,50,60,70,80,90,100}

IfsearchValue is 60, the

method will return 5 to Search

method.

40

10

20

30

50

60

70

80

90

100

num[0]

num[1]

num[2]num[3]

num[4]

num[5]

num[6]

num[7]

num[8]

num[9]

Location, i

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Calculation in array

Eg:- add a number from Array1 and Array2,

and store the total in Array3

Assume Array1, Array2 and Array3

declarations as below:

int[ ] Array1 = {10,20,30,40,50,60,70,80,90,100};

int[ ] Array2 = {11,22,33,44,55,66,77,88,99,110};

int[ ] Array3 = new int[10];

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+

10 2142

63

84

:

:

:

::

:

1120

30

40

50

60

70

8090

100

22

33

44

55

66

77

8899

110

Array[0]Array[1]

Array[2]

Array[3]

Array[4]

Array[5]

Array[6]

Array[7]Array[8]

Array[9]

Array[0]Array[1]

Array[2]

Array[3]

Array[4]

Array[5]

Array[6]

Array[7]Array[8]

Array[9]

Array[0]Array[1]

Array[2]

Array[3]

Array[4]

Array[5]

Array[6]

Array[7]Array[8]

Array[9]

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public static void ArraySum()

{

int[] Array1 = {10,20,30,40,50,60,70,80,90,100};

int[] Array2 = {11,22,33,44,55,66,77,88,99,110};

int[] Array3 = new int[10];

int i;

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

{

Array3[i] = Array1[i] + Array2[i];

System.out.println("Array3["+i+"]=

+Array3[i]);

}

}

Output

Array3[0] = 21

Array3[1] = 42Array3[2] = 63

Array3[3] = 84

Array3[4] = 105

Array3[5] = 126Array3[6] = 147

Array3[7] = 168

Array3[8] = 189

Array3[9] = 210

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

Array3[i] = Array1[i] + Array2[i];

Values of Array3 during for loop iterations

i Array1[i] Array2[i] Array3[i]

0 10 11 21

1 20 22 422 30 33 63

3 40 44 84

4 50 55 105

5 60 66 126

6 70 77 147

7 80 88 168

8 90 99 189

9 100 110 210

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Reverse element

Eg- Read 10 integer numbers, and print the

numbers in reverse order

public static void ReverseOrder()

{

int item[] = new int[10];

int i;//Read integers number and store in item[i]

System.out.println("Enter ten integers number:");

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

item[i] = input.nextInt();

//Print the output in reverse order are:");System.out.println("The numbers in reverse order are:");

for(i = 9; i >= 0; i--)

System.out.println(item[i]);

}

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Output Enter ten integers number:56

65

67

4364

76

39

77

47

84The numbers in reverse order are:

84

47

77

39

76

64

43

67

65

56

A F l P t t M th d

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Arrays as Formal Parameters to Methods

Arrays can be passed as parameter to methods

Eg.

public static void arrayAsFormalParameter(int[] listA,

double[] listB, int num)

{

//

}

Formal parameter

The above method have 3 formal parameterslistA,

listB and num

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continue

Statement to call the method

arrayAsFormalParameter(intList, doubleNumList, number);

Actual parameter

int[] intList = new int[10];

double[] doubleNumList = new double[15];

int number;

Suppose we have the following statement

example 1

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example 1public class PassingParameter {

public static void main(String[] args)

{

int num[] = {10,20,30,40,50,60,70};

System.out.println( The number of elements: "+ num.length);

printArray(num);

}

public static void printArray(int[] number)

{for (int index = 0; index < number.length; index++)

System.out.println(number[index] + "");

}

}

Passing parameter

OUTPUT:

The number of elements: 7

10

20

30

40

50

60

70

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public static void main(String[] args)

{

int[] listA = {11,22,36,42,15,46,27,48,19,10}

int[] listB = new int[10];

int Total, Largest;

// call sumArray method and return a value to Total

Total = sumArray (listA, listA.length);

System.out.println(\n The sum of ListA is :+ Total);

// call indexLargestElement and return the indux value to Largest

indLargest = indexLargestElement (listA, list.length);

System.out.println(\n The largest element is : + listA[Largest]);

example 2

continue

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public static int sumArray(int[] list, int noOfElements)

{

int index;

int sum = 0;

for (index = 0; index < noOfElement; index++)

sum = sum + list[index];

return sum;

}

public static int indexLargestElement(int[] list, int noOfElement)

{

int index;

int maxIndex = 0;

for (index = 1; index < noOfElement; index++)

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

maxIndex = index;return maxIndex;

}

Array of String Objects

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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 Object

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Array of Object

Can use arrays to manipulate objects.

Example: Create an array named array1 with Nobject 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();

Eg:a) clock hour, minute, secondb) student name, matric, age

example

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import java.util.*;

public class ArrayOfObj {

int N = 3;

StudentInfo[] student = new StudentInfo[N];

public static void main (String[] args)

{

int N = 3;

int i;

ArrayOfObj arr = new ArrayOfObj();

StudentInfo[] Std = new StudentInfo[N];

Std = arr.InputData();

arr.PrintInfo(Std);

}

example

Input students information's (name,matric, age) into array and print out the output

class StudentInfo{

String name;

String matric;

int age;

}

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public StudentInfo[] InputData()

int i;

StudentInfo[] student = new

StudentInfo[N];

System.out.println("\nEnter Students

Information ");

System.out.println("_______________________

____ \n");

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

{

student[i] = new StudentInfo();

System.out.print("Name : ");

student[i].name = input.readLine();

System.out.print("Matric No : ");

student[i].matric = input.nextLine();

System.out.print("Age : ");

student[i].age = input.nextInt();

System.out.println();

}

return student;

}

public void PrintInfo(StudentInfo[] Std)

{

int i;

System.out.println("List of students

:\n");

for (i=0;i

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Enter Students Information___________________________

Name : BAHARUDIN OSMAN

Matric No : S11111

Age : 30

Name : BADRUL HAZMI

Matric No : S23212Age : 28

Name : NUR BADRINA

Matric No : S34213

Age : 27

List of students :

1. S11111 BAHARUDIN OSMAN 30

2. S23212 BADRUL HAZMI 28

3. S34213 NUR BADRINA 27

output

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Statement below create an array of arrivalTimeEmp

Clock[] arrivalTimeEmp = new Clock[100];

Instantiating of Array Objects

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Instantiating of Array Objects

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

arrivalTimeEmp[j] = new Clock();

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Continue

Setting a time for index 49

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

T o Dimension Arra

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Two-Dimension Array

A collection of a fixed number of components

arranged in rows and columns. All components are in same type.

Data is sometimes in table form (difficult to representusing a one-dimensional array).

10 11 21 45

20 22 42 34

30 33 66 21

40 44 84 32

50 55 105 13

60 66 126 21

70 77 147 33

80 88 168 22

90 99 189 123

continue

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continue

To declare/instantiate a two-dimensional array:

dataType[ ][ ] arrayName = new data Type[intRow][intCol];

intRow => number of rowsintCol => number of columns

intRow and intCol > 0

Eg.

double[ ][ ] sales = new double[10][15];

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

Accessing Array Components

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Accessing Array Components

To access a component of a two-dimensional array:

arrayName[indexExp1][indexExp2];

indexExp1 = row position

indexEXp2 = column position

Eg.

The above statement stores 25.75 into row number 5 and columnnumber 3; (the 6th row and the 4th column)

sales [5][3] = 25.75;

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Sales [5][3] = 25.75;

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Array Initialization During Declaration

2-Dimensional array can be initialized during declaration

Eg.

int[ ][ ] board = { {2,3,1},

{15,25,13},

{20,4,7},{11,18,14}};

P i 2 Di i l A

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Processing 2-Dimensional Array

eg.

Initialization Print

Input data/store data into 2-Dimensional array

Sum the data

Find the largest element

Suppose the declaration as below:

int row;

int column;

int matix = new int[7][6];

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Initialization

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

for (col = 0; col < matrix[row].length; col++)matrix[row][col] = 10;

matrix

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Print

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

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

System.out.println(matrix[row][col]);

System.out.println();

}

Read Data


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

matrix[row][col] = Integer.parseInt(keyboard.readLine())

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Sum by Row


{ sum = 0;


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

System.out.println(Sum of row+ (row + 1) + = + sum);

}

Sum by Column

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

{

sum = 0;


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];


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

largest = matrix[row][col];

System.out.println(The largest element of row+ (row+1)

+=+ largest);

}

M ltidi i l A

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Can define three-dimensional arrays or n-dimensional arrays (ncan 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

Multidimensional Arrays

Loops to Process Multidimensional Arrays

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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;

Loops to Process Multidimensional Arrays

basic - week 11 & 12

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