1. indexOf的参数是 String,  startIndex: Number;

indexOf的返回值为int,

2. Function indexOf 包含如下几个格式：

1). Strng.indexOf(substring) //搜索String中的substring,默认从0位开始；

2). String.indexOf(substring, int m) //搜索String中的substring, 默认从第m位开始；

Sample:

取IP地址的第一个代码段：

int p;

int q;

String inputIP = null;

String IPsection1 = null;

String IPsection2 = null;

inputIP = "1.100.1.1";

p = inputIP.indexOf('.');

q = inputIP.indexOf('.',p+1);

IPsection1 = inputIP.substring(0,p);

IPsection2 = inputIP.substring(p+1, q);

System.out.println("the 1st IP section is "+IPsection1);

System.out.println("the 2nd IP section is "+IPsection2);

输出结果为

the 1st IP section is 1

the 2nd IP section is 100