public static Direction getDirectionByLeeter(final char letter) throws NotValidDirectionException{
		switch(letter){
			case 'N' : return NORTH ;
			case 'E' : return EAST ;
			case 'W' : return WEST ;
			case 'S' : return SOUTH ;
			
			default : throw new NotValidDirectionException();//no valid direction
		}
	}