The document discusses arrays in Java programming. It covers topics like declaring and initializing one-dimensional and multi-dimensional arrays, processing array data through loops and methods, and common operations on arrays like initialization, input, output, and finding maximum/minimum values. The document also discusses passing arrays as parameters to methods and using arrays to store objects.

1. Java Programming: From Problem Analysis to Program Design, 3e Chapter 9 Arrays

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

3. Chapter Objectives (continued) 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. Array Definition: structured data type with a fixed number of elements Elements of an array are also called components of the array Every element is of the same type Elements are accessed using their relative positions in the array

5. One-Dimensional Arrays

6. One-Dimensional Arrays (continued)

7. One-Dimensional Arrays (continued) intExp = number of components in array >= 0 0 <= indexExp <= intExp

8. Array num: int[] num = new int[5]; Arrays

9. Array List

10. Array List (continued)

11. Array List (continued)

12. Array List (continued)

13. Specifying Array Size During Program Execution

14. The initializer list contains values, called initial values , that 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 Array Initialization During Declaration

15. Array Initialization During Declaration (continued) 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

16. Associated with each array that has been instantiated, there is a public ( final ) instance variable length 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}; Arrays and the Instance Variable length

17. Arrays and the Instance Variable length (continued) This statement creates the array list of six components and initializes the components using the values given Here list.length is 6 int [] numList = new int[10]; This statement creates the array numList of 10 components and initializes each component to 0

18. The value of numList.length is 10 numList[0] = 5; numList[1] = 10; numList[2] = 15; numList[3] = 20; These statements store 5 , 10 , 15 , and 20 , respectively, in the first four components of numList You can store the number of filled elements, that is, the actual number of elements, in the array in a variable, say numOfElement 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 (continued)

19. 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] + &quot; &quot;); Processing One-Dimensional Arrays

20. Arrays (continued) 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;

21. Code to Initialize Array to Specific Value (10.00) for (index = 0; index < sales.length; index++) sales[index] = 10.00;

22. Code to Read Data into Array for (index = 0; index < sales.length; index++) sales[index] = console.nextDouble();

23. Code to Print Array for (index = 0; index < sales.length; index++) System.out.print(sales[index] + &quot; &quot;);

24. 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;

25. Determining Largest Element in Array maxIndex = 0; for (index = 1; index < sales.length; index++) if (sales[maxIndex] < sales[index]) maxIndex = index; largestSale = sales[maxIndex];

26. Determining Largest Element in Array (continued)

27. Determining Largest Element in Array (continued)

28. Array Index Out of Bounds Array in bounds if: 0 <= index <= arraySize – 1 If index < 0 or index > arraySize : ArrayIndexOutOfBoundsException exception is thrown Base address: memory location of first component in array

29. Declaring Arrays as Formal Parameters to Methods A 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);

30. The Assignment Operators and Arrays

31. The Assignment Operators and Arrays (continued)

32. The Assignment Operators and Arrays (continued)

33. Relational Operators Arrays if (listA == listB)... - The expression listA == listB determines if the values of listA and listB are the same and thus determines 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

34. Relational Operators and Arrays (continued) 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)) ...

35. Arrays as Parameter Methods

36. Methods for Array Processing

37. Methods for Array Processing (continued)

38. Methods for Array Processing (continued)

39. Methods for Array Processing (continued)

40. Parallel Arrays Arrays are parallel if corresponding components hold related information

41. Arrays of Objects Can use arrays to manipulate objects Example: create 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();

42. Array of String Objects String[] nameList = new String[5]; nameList[0] = &quot;Amanda Green&quot;; nameList[1] = &quot;Vijay Arora&quot;; nameList[2] = &quot;Sheila Mann&quot;; nameList[3] = &quot;Rohit Sharma&quot;; nameList[4] = &quot;Mandy Johnson&quot;;

43. Array of String Objects (continued)

44. Clock[] arrivalTimeEmp = new Clock[100]; Arrays of Objects (continued)

45. Instantiating Array Objects for ( int j = 0; j < arrivalTimeEmp.length; j++) arrivalTimeEmp[j] = new Clock();

46. arrivalTimeEmp[49].setTime(8, 5, 10); Instantiating Array Objects (continued)

47. Arrays and Variable Length Parameter List The syntax to declare a variable length formal parameter (list) is: dataType ... identifier

48. Arrays and Variable Length Parameter List (continued)

49. Arrays and Variable Length Parameter List (continued)

50. Arrays and Variable Length Parameter List (continued) A method can have both a variable length formal parameter and other formal parameters; consider the following method heading: public static void myMethod(String name, double num, int ... intList) The formal parameter name is of type String , the formal parameter num is of type double , and the formal parameter intList is of variable length The actual parameter corresponding to intList can be an int array or any number of int variables and/or int values

51. Arrays and Variable Length Parameter List (continued) A method can have at most one variable length formal parameter If a method has both a variable length formal parameter and other types of formal parameters, then the variable length formal parameter must be the last formal parameter of the formal parameter list

52. 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

53. foreach loop (continued) 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; }

54. Two-Dimensional Arrays

55. Two-Dimensional Arrays (continued)

56. double [][] sales = new double [10][5]; Two-Dimensional Arrays (continued)

57. intExp1, intExp2 >= 0 indexExp1 = row position indexExp2 = column position Accessing Array Elements

58. Accessing Array Elements (continued)

59. This statement declares and instantiates a two-dimensional array matrix of 20 rows and 15 columns The value of the expression: matrix.length is 20, the number of rows Two-Dimensional Arrays and the Instance Variable length

60. Two-Dimensional Arrays and the Instance Variable length (continued) Each row of matrix is a one-dimensional array; matrix[0] , in fact, refers to the first row The value of the expression: matrix[0].length is 15, the number of columns in the first row matrix[1].length gives the number of columns in the second row, which in this case is 15, and so on

61. Two-Dimensional Arrays: Special Cases

62. Two-Dimensional Arrays: Special Cases (continued) Create columns

63. Two-Dimensional Array Initialization During Declaration

64. Two-Dimensional Array Initialization During Declaration (continued) To initialize a two-dimensional array when it is declared - The elements of each row are enclosed within braces and separated by commas - All rows are enclosed within braces

65. Two-Dimensional Array Initialization During Declaration (continued)

66. Two-Dimensional Arrays (continued) Three ways to process 2-D arrays Entire array Particular row of array (row processing) Particular column of array (column processing) Processing algorithms similar to processing algorithms of one-dimensional arrays

67. 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(&quot;%7d&quot;, matrix[row][col]); System.out.println(); }

68. Two-Dimensional Arrays: Processing (continued) 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(&quot;Sum of row &quot; + (row + 1) + &quot; = &quot;+ sum); }

69. Two-Dimensional Arrays: Processing (continued) 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(&quot;Sum of column &quot; + (col + 1) + &quot; = &quot; + sum); }

70. Two-Dimensional Arrays: Processing (continued) 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(&quot;The largest element of row &quot; + (row + 1) + &quot; = &quot; + largest); }

71. Two-Dimensional Arrays: Processing (continued) 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(&quot;The largest element of col &quot; + (col + 1) + &quot; = &quot; + largest); }

72. Multidimensional Arrays Can define three-dimensional arrays or n-dimensional array (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

73. 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;

74. 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 letter appears in text

75. Programming Example Solution: Text Processing An array of 26 representing the letters in the alphabet Three methods copyText characterCount writeTotal Value in appropriate index incremented using methods and depending on character read from text

76. Chapter Summary Arrays Definition Uses Different Arrays One-dimensional Two-dimensional Multidimensional (n-dimensional) Arrays of objects Parallel arrays

77. Chapter Summary (continued) Declaring arrays Instantiating arrays Processing arrays Entire array Row processing Column processing Common operations and methods performed on arrays Manipulating data in arrays