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Chapter 9: Arrays

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

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  1. Chapter 9: Arrays JavaProgramming: 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. Array num int[] num = new int[5]; Java Programming: From Problem Analysis to Program Design, Second Edition

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

  8. 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

  9. 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

  10. 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

  11. 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

  12. 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

  13. 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

  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 = newint[10]; double[] doubleNumList = newdouble[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. 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

  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. 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

  29. 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

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

  35. 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

  36. Instantiating Array Objects arrivalTimeEmp[49].setTime(8, 5, 10); 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. Two-Dimensional Arrays double[][]sales = new double[10][5]; 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; 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

  48. 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

  49. 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

  50. 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

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