public static String strStr(String haystack, String needle) {
        if (null == haystack || null == needle) return null;
        if ("".equals(needle)) return haystack;
        for (int i = 0; i <= haystack.length() - needle.length(); i++) {
        	int t = i;
        	int j = 0;
        	for (j = 0; t < haystack.length() && j < needle.length(); j++, t++) {
        		if (haystack.charAt(t) != needle.charAt(j)) break;
        	}
        	if (j == needle.length()) return haystack.substring(i); 
        }
    	return null;
    }