public void setOperator(String operator) {
		/** Operators consist of: ( ) + - * / =
		 * If input is not part of the above operators, then this.operator is null
		 */
		if (( operator.equals(" ") || operator.equals("(") || operator.equals(")") || operator.equals("+") ||
				operator.equals("-") || operator.equals("*") || operator.equals("/") ||
				operator.equals("=")))
			this.operator = operator;
		else
			System.out.println("Invalid Operator");
	}