java - How to use charAt() and length() to write a whether is substring method -

i want write boolean method substring() judge if string s1 substring of s2.

the requirement use charat() and length() methods of string.

e.g.

 substring("abc","abcd")-> true   substring("at","cat")->true   substring("ac","abcd")->false 

indexof() cannot used.

here got far.

public class q3 {     public boolean substring(string str1, string str2) {         string s1 = str1.tolowercase();         string s2 = str2.tolowercase();         (i = 0; < s1.length; i++) {             (j = 0; j < s2.length; j++) {                 if (s1.charat(i) == s2.charat(j))                     return true;             }         }         return false;     } } 

test class :

public class q3test {     public static void main (string arg[]){         q3 q3object = new q3();         system.out.println(q3object.substring("ac","abcd"));     } } 

it fails substring("ac","abcd") returns true.

your code returns true if first character matches. need characters of first string contained in substring of second string.

edit:

my original code wrong. here's correct code :

        public static boolean substring(string str1, string str2)         {           string s1 = str1.tolowercase();           string s2 = str2.tolowercase();           (int offset = 0; offset <= s2.length() - s1.length(); offset++) {             int = 0;             (; < s1.length(); i++){               if(s1.charat(i) != s2.charat(i+offset)) {                 break;               }             }             // found substring starts @ current offset             if (i == s1.length())               return true;           }           return false;         }