public String encrypt  (String word) {
	if(word == null||word.length()==0) throw new IllegalArgumentException();
	String result = "";
	String wordLower = word.toLowerCase();
	for(int i=0; i<wordLower.length(); i++){
	    if(wordLower.charAt(i)<97 || wordLower.charAt(i)>122)
		throw new IllegalArgumentException();
	    int k = (((wordLower.charAt(i)-97)+this.cipherKey)%26)+97;
	    result += Character.toString((char)k);
	}
	return result;
    }