java startsWith和endsWith的用法

public class StringDemo{

public static void main(String args[]){
String s1="this is my original string";
String sd="original";
if (s1.startsWith(sd))
//startsWith()方法判断字符串s1是否从字符串sd开始
s1=s1.substring(sd.length());
else
if(s1.endsWith(sd))
//endWith()方法判断字符串s1是否从字符串sd结尾
s1=s1.substring(0,s1.length()-sd.length());
else
{
int index=s1.indexOf(sd);
//indexOf()搜索字符或子字符串首次出现，这里的index等于11
if(index!=-1)
{
String s2=s1.substring(0,index);
//从字符串s1的首字符开始，取index个字符
String s3=s1.substring(index+sd.length());
//取字符串s1的第19个字符后面的字符串
s1=s2+s3;
}
else
System.out.println("string /""+sd+"/" not found");
}
System.out.println(s1);
}