lect6arrays_4up

# lect6arrays_4up - CMPT 126 Lecture 6 Arrays Tamara Smyth...

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Unformatted text preview: CMPT 126: Lecture 6 Arrays Tamara Smyth, [email protected] School of Computing Science, Simon Fraser University September 25, 2007 1 Array Elements • An array is a construct used to group and organize data. • By using an array, we don’t have to declare separate variables for large amounts of data. • An array is a list of values of the same type, each one stored at a specific numbered position called an index . array elements 5 4 3 2 1 indeces 88 78 32 42 67 4 Figure 1: An array. • An array of size N is indexed from 0 to N- 1 . CMPT 126: Arrays, Lecture 6 2 Declaring and Using Arrays • In Java, an array is an object that must be instantiated. To create an array, the reference to the array must be declared: int height = new int[11]; where the variable is height , which is declared to be an array of eleven integers. • The instantiation of height , using the new operator, reserves the memory space to store 11 integers. • The size of an array cannot be changed. • To access a value in an array, we use the name of the array followed by the index in square brackets: height[2] = 45; CMPT 126: Arrays, Lecture 6 3 Initializer list • The array may also be initialized at declaration using an initializer list , in which case the new operator is not used: int height = {2, 34, 45, 22, 235}; • An initializer list can only be used when an array is first declared. • The type of each value in the initializer list must match the array element type. CMPT 126: Arrays, Lecture 6 4 PrintArray.java • It is often convenient to use for loops when handling arrays because the number of positions in the array is constant. public class PrintArray { public static void main(String args) { final int LIMIT = 15, MULTIPLE = 10; int list = new int[LIMIT]; // initialize the array values for (int i = 0; i< LIMIT; i++) list[i] = i * MULTIPLE; list[5] = 999; //change one value // Print the array values for (int value : list) System.out.print(value + " "); } } • Every Java array is an iterator so the version of for that extracts each value in the specified iterator may be used. CMPT 126: Arrays, Lecture 6 5 Bounds Checking • Bounds checking ensures that an index used to refer to an array element is in range. • The index operator performs automatic bounds checking , though we will still want to perform our own bounds checking. • A reference to an array must be greater than or equal to zero , and less than the size of the array . • The length of the array may be determined using its length constant....
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lect6arrays_4up - CMPT 126 Lecture 6 Arrays Tamara Smyth...

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