java.util.regex.PatternSyntaxException:在索引0 +附近悬挂元字符'+'

Question

当我启动我的UI导致此代码在标题中向我吐出错误时,我收到错误.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,所以你可以在我的gitHub上找到其余的代码: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,你应该看看这些字符以达到你想要的效果.例如,你不能使用String.split("+"),你必须使用String.split("\\+").

正确的运算符是:

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

Answer 2

在您的情况下，+ *并被^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其参数并返回一个String数组。为避免将上述视为元字符，您需要在代码中使用这些转义序列"\\+" "\\*" "\\^"

像这样修改您的运算符数组

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

有关更多详细信息，请参阅这些链接regex.Pattern和 String.split()