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