先上代码，以截取固话区号及不含区号的号码为例：
1 public class TestSubstring {
2 public static void main(String[] args) {
3 String phoneNbr="05718888888";
4 //对于4位区号应该是substring(0,4)，不是substring(0,3)
5 System.out.println(phoneNbr.substring(0,4)+" "+phoneNbr.substring(4));
6 }
7 }
java API 中的说明：
Returns a new string that is a substring of this string. The substring begins at the specified beginIndex and extends to the character at index endIndex - 1. Thus the length of the substring is endIndex-beginIndex.
Examples:
"hamburger".substring(4, 8) returns "urge"
"smiles".substring(1, 5) returns "mile"
Parameters:
beginIndex the beginning index, inclusive.
endIndex the ending index, exclusive.