public ArrayList<expressionElement> convertToPostfix(ArrayList<expressionElement> infix){
        ArrayList<expressionElement> postfix = new ArrayList<expressionElement>();
        ArrayDeque<expressionElement> ops = new ArrayDeque<expressionElement>();

        for(expressionElement element : infix){
            if(element.getType().equals("int") || element.getType().equals("double")){ // IS a number
                postfix.add(element);
            }
            else{ // IS an operator
                // This next if tests if it's the stack is empty, or if it's something that we can push, regardless
                if (ops.size() == 0 || ops.peekLast().getOperator().equals("(") || element.getOperator().equals("(")) {
                    ops.push(element);
                }
                else{
                    // Using this table: http://en.wikipedia.org/wiki/Operators_in_C_and_C%2B%2B#Operator_precedence
                    int currPrecedence = getPrecedence(element.getOperator());

                    while (ops.size() != 0 && currPrecedence <= getPrecedence(ops.peekLast().getOperator())) {
                        postfix.add(ops.removeLast());
                    }
                    ops.push(element);
                }
            }
        }