public boolean set_hhmm(String hhmm) {
    	if(hhmm.matches("\\d\\d\\d\\d")) {
    		int h= (byte)Integer.parseInt(hhmm.substring(0, 2));
    		int m= (byte)Integer.parseInt(hhmm.substring(2, 4));
			if(h>=0 && h<24 && m>=0 && m<60) {
				this.hour=(byte) h;
				this.minute=(byte) m;
				return true;
			}
    	}
    	return false;
    }