TR-Java-lecture04-array.ppt

Java程序设计 Java Programming Spring, 2009 Contents Arrays(数组) Arrays (数组) An array is a collection of data values, all of which have the same type. Components: Primitive types or reference to objects Arrays are objects in Java(数组是一种特殊的对象) Declaring Arrays(声明数组) An array variable is declared with the type of the members. 一维数组的声明 方法1: 类型 数组名[]; String args[]; int a[]; double amount[]; char c[]; 方法2: 类型[] 数组名; String[] args; int[] a; double[] amount; char[] c; Declaring Arrays(声明数组) 注意 数组类型是数组中元素的数据类型； 数组名是一个标识符； When an array variable is declared, the array is NOT created. What we have is only a name of an array. Creating Arrays(创建数组) 为数组元素分配内存空间，并对数组元素进行初始化 To create the array, operator new is used. We must provide the number of members in the array, and the type of the members. These cannot be changed later. 格式: 数组名 = new 数据类型[数组长度] Example: or, combining the declaration and the array creation: Creating Arrays(创建数组) 默认赋初值 整型?初值为0 int[] i = new int[3]; 实型?初值为0.0 float[] f = new float[3]; 布尔型?初值为false boolean[] b = new boolean[3]; 字符型?初值为\u0000(null) char[] c = new char[3]; Accessing(访问) array members Array members are accessed by indices using the subscript operator []. The indices are integers starting from 0. In Java, for an array of length n, the values in the array are indexed from 0 up to n – 1. If an index is out of range, i.e., less than 0 or greater than length-1, a run-time error occurs. Initializing(初始化) array members 为数组元素指定初始值 方式1 : Array members may also be initialized when the array is created(在创建数组的同时对数组元素初始化): int[] intArray; intArray = new int[]{ 3, 5, 4 }; 方式2: 声明和创建数组后对数组初始化 Example 1: Array members can be initialized individually using the indices and the subscript operator. int[] intArray = new int[3]; intArray[0] = 3; intArray[1] = 5; intArray[2] = 4; Initializing(初始化) Example 2: When an array is created, the number of positions available in the array can be accessed using a field called length w