两个字符串的最长公共字串

public static String maxCommonStr(String s1, String s2){
    String maxStr = "";
    for (int end= 1, begin = 0; end <= s1.length();){
        String str = s1.substring(begin, end);
        if(s2.contains(str)){
            maxStr = str.length() > maxStr.length()? str : maxStr;
            end++;
        }else{
            begin++;
            if(begin == end)end++;
        }
        
    }
    return maxStr;
}