Notes

Outline

COM 1100 1/22/02 Class 8

Today’s class Array Declaration Array Initialization Multidimensional Arrays Accessing arrays Codewarrior demonstration Lab discussion

Array Declaration int num[]; num = new int[256]; Once an array is created, its size cannot be changed int num[256]; This will NOT work Will work in C and C++, but not in Java

Array Initialization int b[] = { 0, 1, 2, 3, 4}; String wkdays[] = {“Mon”, “Tue”, “Wed”, “Thu”, “Fri”}; Declares the array and initialize it one step

Multidimensional Arrays A Multidimensional Array is sometimes called an array of arrays Can be visualized as a 2-d table, or 3-d cube Arrays do not have to be the same size int num[][] = new int[124][256];

Sample Initializations int myTable[][] = new int[][]{ new int[] {0}, new int[] {0,1}, new int[] {0,1,2}}; int myTable[][] = new int[][]{ {0}, {0,1}, {0,1,2}};

Movable Brackets The brackets in an array declaration can move around Traditionally, they follow the variable name, but this is not a requirement in the language The following are all valid array declarations: Int a[]; Int [] b = {a.length, 2, 3}; Char c [] [] = new char[12][32]; Char[] [] e;

Accessing Array Elements An element stored in an array is accessed by its subscript The element stored in position 24 of array num would be accessed by num[24] Arrays are all accessed numerically To access an element in a 2-d array you need two numbers Num[12] [24] would return the element stored in position 24 of the array stored

Array Index Starts at Zero All array indexes start at zero An array with 256 elements can be accessed from num[0] to num[255] Trying to access num[256] in this array will return an array out of bounds error

Finding Array Size You may not always know the size of the array you are passed in a function Java provides a data field built into every array to tell you how many elements are stored in it arrayname.length will return the number of elements stored in the array

Cloning an Array Sometimes you may need to copy an array for one reason or another Java provides a function to make this easier int newarray[] = (int []) oldarray.clone(); Simply copies all the elements of the old array into the new array Arrays are the same size

Copying part of an array To copy part of an array from one array to another, use the System.arraycopy() function Syntax: System.arraycopy(source_array, offset, dest_array, offset, length) Will not work for multidimensional arrays, only for single arrays

Creation of a Project in Codewarrior Demonstration of how to create a project in Codewarrior

Discussion of New Lab Demo and discussion of Lab assigned for this week