leetcode Implement strStr()(easy) /java

import java.io.*;
import java.util.*;

public class Solution {
        public static int strStr(String haystack, String needle) {
        int r=-1;
        int len1=haystack.length();
        int len2=needle.length();
        if(len2==0)
            return 0;
        int len=len1-len2+1;
        int i,j;
        String s;
        for(i=0;i<len;i++)
        {
            s=haystack.substring(i,i+len2);
            if(s.matches(needle))
            {
                r=i;
                break;
            }
        }
        return r;
    }
    public static void main(String[] args)
    {

        System.out.println(strStr("ababcd","cd"));
        System.out.println(strStr("abcdab","ef"));
    }
}