Question

当我启动我的UI时，我收到错误导致此代码在标题中向我吐出错误。它适用于我所有其他运算符符号，所以我真的不确定这里发生了什么。我不想发布所有代码，这样如果我的gitHub上的内容不够，我就可以找到其他代码：https://github.com/jparr721/Calculator-App/tree/master/src/calculator

public class Calculation_Controls {

    public double A, B;

    private String[] operators = new String[] {"-","+","/","*","x","^","X"};


    /**
     * Check for the symbol being used within the TextArea to then
     * apply the correct caculation method.
     * FIXME - Allow for multiple symbols to be used and have them return
     * FIXME - a result in accordance with PEMDAS
     *
     *@param nums
     *
     * @return operator, or error
     */
    public String findSymbol(String nums) {

        for (String operator : operators) {
            if (nums.contains(operator)) {
                return operator;
            }
        }
        return "invalid input";
    }

    /**
     * Input method to take the user input from the text area
     * and apply the correct calculation to it
     *
     * @param nums - Stores the input as a String which I then convert to an int
     *             then back to a string to be printed to the TextArea
     *
     * @return - The result of the calculation as a string
     */
    public String input(String nums){

        String operator = findSymbol(nums);
        if (operator == null){
            System.out.println("Invalid input");

        }
        String[] split = nums.split(operator);
        int left = Integer.parseInt(split[0]);
        int right = Integer.parseInt((split[1]));
        String result = "";

        switch (operator){

            case "+":
                result = Double.toString(add(left, right));
                break;
            case "-":
                result = Double.toString(subtract(left, right));
                break;
            case "*":
            case "x":
            case "X":
                result = Double.toString(multiply(left, right));
                break;
            case "/":
                result =  Double.toString(divide(left, right));
                break;
            case "^":
                result =  Double.toString(pwr(left, right));
                break;
            default:
                System.out.println("Invalid Operator");
        }
        return result;
    }

Answer 1

正则表达式中有保留字符，你应该将这些角色视为实现你想要的。例如，您无法使用String.split("+")，必须使用String.split("\\+")。

正确的运算符是：

    String[] operators = new String[] {"-","\\+","/","\\*","x","\\^","X"};

Answer 2

在您的情况下+ *和^被视为具有特殊含义，通常称为元字符。 String.split()方法将正则表达式作为参数，并返回String数组。为避免将上述内容视为元字符，您需要在代码中使用这些转义序列"\\+" "\\*" "\\^"

像这样修改你的运算符数组

private String[] operators = new String[] {"-","\\+","/","\\*","x","\\^","X"};

更多信息请参阅这些链接regex.Pattern和String.split()

Answer 3

split（）方法使用正则表达式。 '+'符号是正则表达式中的特殊字符，因此您需要使用反斜杠符号（'\'）将其转义。但是你还需要在java中转义反斜杠符号，所以你需要两个反斜杠，例如： “\\ +”

Answer 4

更改：String[] split = nums.split(operator);

对此：String[] split = nums.split("\\" + operator);

编辑：这只适用于标准运算符，而不适用于x或X.您必须实际更改String[] operators声明，就像上面提到的其他答案一样。就个人而言，我会进行某种输入验证，并在x或X上执行replace（）而不是*

Answer 5

您可以使用 case String.valueOf（'+'）;

java.util.regex.PatternSyntaxException：悬空元字符＆＃39; +＆＃39;接近指数0 +

5 个答案: