private String calculatePostfix(QueueInterface<T> postfix) throws DAIndexOutOfBoundsException, DAIllegalArgumentException, NumberFormatException, NotEnoughOperandsException
	{
		StackInterface<T> operandStack = new DynamicArray<T>();
		DequeInterface<T> exprDeque = new DynamicArray<T>();
		String result = "";
		
		while(postfix.getSize() != 0)
		{
			String currentItem = (String) postfix.getFront();
			
			if(currentItem.matches(OPERAND))
			{
				operandStack.addLast(postfix.removeFront());
			}
			else if(currentItem.matches(OPERATOR))
			{
				if(operandStack.getSize() >= 2)
				{
					exprDeque.addLast(operandStack.removeLast()); //adding last operand in expression
					exprDeque.addFront(postfix.removeFront()); //adding the operator
					exprDeque.addFront(operandStack.removeLast()); //adding first operand in expression
					operandStack.addLast(calculateExpr(exprDeque)); //adding the result to the stack
				}
				else
				{
					throw new NotEnoughOperandsException();
				}
			}
		}
		if(operandStack.getSize() == 1)
			result = (String) operandStack.removeLast();
		return result;
	}