1. Lecture 9 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

2. Lecture 9 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

3. 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

4. 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
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5. Array num int[] num = new int[5];
Java Programming: From Problem Analysis to Program Design, Second Edition

6. Array list
Java Programming: From Problem Analysis to Program Design, Second Edition

7. 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

8. 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]=
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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9. 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

10. 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.
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11. 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
list[i] = console.nextInt();
System.out.print(list[i] + " ");
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12. 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;
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13. 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

14. 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

15. 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

16. Code to Find Sum and Average of Array
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

17. 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

18. Determining Largest Element in Array
Java Programming: From Problem Analysis to Program Design, Second Edition

19. 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.
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20. 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);
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21. The Assignment Operators and Arrays
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
for (int index = 0; index < listA.length; index++) listB[index] = listA[index];
Java Programming: From Problem Analysis to Program Design, Second Edition

24. 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

25. 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 true; }
if (isEqualArrays(listA, listB))
...
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26. 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

27. 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 sum = 0;
sum = sum + list[index];
return sum;
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28. 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,
for (index = 0; index < noOfElements; index++)
list2[index] = list1[index];
Java Programming: From Problem Analysis to Program Design, Second Edition

29. Parallel Arrays
Arrays are parallel if the corresponding components hold related information.
Java Programming: From Problem Analysis to Program Design, Second Edition

30. 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

31. 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";
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32. Array of String Objects
Java Programming: From Problem Analysis to Program Design, Second Edition

33. Clock[] arrivalTimeEmp = new Clock[100];
Arrays of Objects
Clock[] arrivalTimeEmp = new Clock[100];
Java Programming: From Problem Analysis to Program Design, Second Edition

34. 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

35. Instantiating Array Objects
arrivalTimeEmp[49].setTime(8, 5, 10);
Java Programming: From Problem Analysis to Program Design, Second Edition

36. 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

37. 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

38. 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

39. 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

40. 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

41. 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
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42. 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

43. 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

44. Accessing Two-Dimensional Array Components
Java Programming: From Problem Analysis to Program Design, Second Edition

45. Two-Dimensional Arrays: Special Cases
Java Programming: From Problem Analysis to Program Design, Second Edition

46. 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

47. 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

48. 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

49. 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

50. 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

51. 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
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52. 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

53. 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.
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54. 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

55. Lecture 8 Summary Arrays Different arrays Definition Uses
One-dimensional
Two-dimensional
Multidimensional (n-dimensional)
Arrays of objects
Parallel arrays
Java Programming: From Problem Analysis to Program Design, Second Edition

56. Lecture 8 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