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

2 Arrays and Variable Length Parameter List public static double largest(double... numList) { double max; int index; if (numList.length != 0) { max = numList[0]; for (index = 1; index < numList.length; index++) { if (max < numList [index]) max = numList [index]; } return max; } return 0.0; }

3 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, , 112.0, 77, 11, 22, 86.62); System.out.println(largest(numberList));

4 Rules to follow when using a variable length formal parameter list: 1.A method can have both a variable length formal parameter and other formal parameter. public static void myMethod (String name, double num, int … intList) 2.A method can have at most one varible length formal parameter. 3.If a method has both a variable length formal parameter and other formal parameter, then the variable length formal parameter must be the last). Arrays and Variable Length Parameter List

5 foreach loop  The most recent version of Java provides a special type of for loop to process the elements of an objects such as an array.  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.  This form of for is called a foreach loop.

6 foreach loop sum = 0; //line1 for (double num : list) //line2 sum = sum + num; //line3  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; }

7 [Red][Brown][Black][White][Gray] [GM] [Ford]63664 [Toyota]35367 [BMW]82753 [Nissan] [Volvo]15797 Two-Dimensional Arrays inStock

8 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

9 double[][]sales = new double[10][5]; Two-Dimensional Arrays

10 Accessing Two-Dimensional Array Components =25.75

11 int [][] matrix = new int[20][15]; 20 rows 15 columns matrix.length = 20 //number of rows  Each row of matrix is 1-D array matrix.[0].length = 15 //# of columns in 1 st row matrix.[1].length = 15 // # of columns in 2 nd row Two-Dimensional Arrays

12 Two-Dimensional Arrays: Special Cases  Can specify different number of columns for each row (ragged arrays). In this case, each row must be instantiated separately.

13 Two-Dimensional Arrays: Special Cases To create this array, first we create 1-D array board of 5 rows: int[] board = new int[5]; board[0] = new int[6]; board[1] = new int[2]; board[2] = new int[2]; board[3] = new int[3]; board[4] = new int[4];

14 Two Dimensional Array Initialization During Declaration int[][] board = {{2,3,1}, {15,25,13}, {20, 4, 7}}; [0][1][2] [0]231 [1] [2]2047 board What is the array created after this statement: int[][] table = {{2,3,1,5}, {15,25}, {4, 23, 45}};

15 Processing Two Dimensional Array  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.  The following declarations are used for our examples: static final int ROWS=7; static final int COLUMNS=6; int[][] matrix = new int [ROWS][COLUMNS]; int row, col, sum, largest, temp;

16  Loop for processing row 5 elements: for (col=0; col < matrix[5].length; col++) //process matrix[5][col]  Loop for processing column 2 elements: for (row=0; row < matrix.length; row++) //process matrix[row][2] Two-Dimensional Arrays: Processing

17 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(); }

18 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); } Two-Dimensional Arrays: Processing

19 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); } Two-Dimensional Arrays: Processing

20 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); } Two-Dimensional Arrays: Processing

21 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); } Two-Dimensional Arrays: Processing

22 Multidimensional Arrays  Can define three-dimensional arrays or n-dimensional arrays (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

23 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;

24 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.

25 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.

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

27 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