Implement strStr

//Implement strStr() Total Accepted: 46286 Total Submissions: 209890 My Submissions Question Solution 
//Implement strStr().
//
//Returns the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.
public class ImplementstrStr {


public static void main(String[] args) {
// TODO 自动生成的方法存根
System.out.print(strStr("mississippi", "pi"));
}
public static int strStr(String haystack, String needle) {
// know length
int len=needle.length();
 if(haystack.length()  return -1;
 if(haystack.length()==len)
 return haystack.equals(needle)?0:-1;
     
     int i;
     //=
     for(i=0;i<=haystack.length()-len;i++){
     boolean a=needle.equals(haystack.substring(i, i+len));
     if(a)
      break;
     }
     if(i<=haystack.length()-len)
     return i;
     return -1;
     
}
}