Chapter 10 Arrays

Learning Java through Alice © Daly and Wrigley Objectives Declare and use arrays in programs. Access array elements within an array. Calculate the sum, largest number, smallest number, and average of a group of numbers by using an array. Setup a program to store the arguments from command line into an array. 2

Learning Java through Alice © Daly and Wrigley Declaring an Array Array - group of contiguous memory locations that all have the same name and the same type. Declaring an array: int [ ] temp; // an integer array called temps boolean[ ] hostilePeople; // an array of hostilePeople String difficultWord [ ]; // an array of difficultWords double examScore[ ]; // an array of examScores 3

Learning Java through Alice © Daly and Wrigley Creating Array Objects int [ ] temp = new int [ 250 ] ; String [ ] reindeerName = { "Dasher", "Dancer", "Prancer", "Vixen", "Comet", "Cupid", "Donner", "Blitzen" } ; 4

Learning Java through Alice © Daly and Wrigley Length of Array String n [ ] = { "Mary", "John", "Susan", "Robert" }; int x = n.length; // where n is the name of the array n[ 0 ] = "Mary" n[ 1 ] = "John" n[ 2 ] = "Susan" n[ 3 ] = "Robert" The length of the array called n is 4. n[2] is "Susan" instead of "John" as you might expect. 5

Learning Java through Alice © Daly and Wrigley Example Array Program public static void main (String args[ ] ){ int number =5; int myArray [ ] = new int[10]; // declares integer array of 10 elements for (int i = 0; i <10; i ++) { myArray[i] = number; // puts 5, 10, 15 into elements of myArray System.out.println("The " + i + " element of the array is " + myArray [ i ] ); number += 5; } The 0 element of the array is 5 The 1 element of the array is 10 The 2 element of the array is 15 The 3 element of the array is 20 The 4 element of the array is 25 The 5 element of the array is 30 The 6 element of the array is 35 The 7 element of the array is 40 The 8 element of the array is 45 The 9 element of the array is 50 6

Learning Java through Alice © Daly and Wrigley Another Way of Writing the Previous Program public static void main (String args[ ] ) { int myArray [ ] = new int[10]; // declares integer array of 10 elements for (int i = 0, number=5; i<10; i ++, number+=5) { myArray[i] = number; // puts 5, 10, 15 into elements of myArray System.out.println("The " + i + " element of the array is " + myArray[i] ); } } 7

Learning Java through Alice © Daly and Wrigley Summing Numbers sum = sum + a; sum= sum + b; sum = sum + c; sum = sum + d; sum = sum + e; OR sum = sum + a + b + c + d + e; OR If the values were in an int array called x, we could do the same thing as follows: for ( i = 0; i < 5 ; i++) { sum = sum + x [ i ]; } 8

Learning Java through Alice © Daly and Wrigley Drawing Polygons 9