Java 尝试捕获导致我的公共void出错的错误

在你提问之前，我已经看了其他问题，它们似乎只是针对稍微不同的事情。 我是java新手，目前正在学习，所以我制作了这个自恋的程序，我将把它制作成一个多工具的东西。那部分其实并不重要。 基本上，我在做一个文本输入计算器，你可以输入数字、运算等等，但它相当简单。然而，在输入区域中，我正在尝试捕捉，以防用户键入非数字的内容。但是，这使得x和y（用户输入）的变量在初始化单独的公共无效计算器（变量）时未初始化且不可读。这是我的代码（我只包括了计算器部分，其余部分都是无关的，工作正常，而且我知道x和y的处理方式不同，我正在测试它们）

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任何帮助都将不胜感激

您应该在try/catch位之外声明变量，如下所示：

double y;

try {
  y = scanner.nextDouble();
catch (Exception e) {
  // Exception handling
}

这应该行得通

import java.util.Scanner;

public class TestSo{
    Scanner scanner = new Scanner(System.in);
    public static void main(String[] args){
        new TestSo().calculatorvariables();
    } 

    public void calculatorvariables() {
        System.out.println("Please enter the first number in your calculation.");

        double x = scanner.nextDouble();
        if(x != (double) x) {
            System.out.println("An error occurred! Did you input nothing or something other than a number? Returning to variable input screen!");
        } else
            System.out.println("Please enter the operator. Valid operators are: '+', '-', '*', '/'");
            String operation = scanner.next();
            System.out.println("Please enter the second number in your calculation.");
            double y = scanner.nextDouble();
            calculator(x, operation, y);
        }
    }

    public void calculator(double x, String operation, double y) {
        if(operation.equals("+")) {
            System.out.println(x + y);
        } else if(operation.equals("-")) {
            System.out.println(x - y);
        } else if(operation.equals("*")) {
            System.out.println(x * y);
        } else if(operation.equals("/")) {
            System.out.println(x / y);
        } else {
            System.out.println("Unknown operation! Returning to input area!");
            calculatorvariables();
        }
        System.out.println("Do you want to do another calculation? Y/N");
        boolean doAnotherCalculation = scanner.next().equalsIgnoreCase("Y");
        if (doAnotherCalculation == true) {
            calculatorvariables();
        } else {
            System.out.println("Done! Exiting");
        }

    }
}

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这就是“声明”变量。这是解决方案的一半。实际上，在

try catch

之外初始化它（即分配一个值）会有更大的帮助。哎呀，我把它修好了。

import java.util.Scanner;

public class TestSo{
    Scanner scanner = new Scanner(System.in);
    public static void main(String[] args){
        new TestSo().calculatorvariables();
    } 

    public void calculatorvariables() {
        System.out.println("Please enter the first number in your calculation.");

        double x = scanner.nextDouble();
        if(x != (double) x) {
            System.out.println("An error occurred! Did you input nothing or something other than a number? Returning to variable input screen!");
        } else
            System.out.println("Please enter the operator. Valid operators are: '+', '-', '*', '/'");
            String operation = scanner.next();
            System.out.println("Please enter the second number in your calculation.");
            double y = scanner.nextDouble();
            calculator(x, operation, y);
        }
    }

    public void calculator(double x, String operation, double y) {
        if(operation.equals("+")) {
            System.out.println(x + y);
        } else if(operation.equals("-")) {
            System.out.println(x - y);
        } else if(operation.equals("*")) {
            System.out.println(x * y);
        } else if(operation.equals("/")) {
            System.out.println(x / y);
        } else {
            System.out.println("Unknown operation! Returning to input area!");
            calculatorvariables();
        }
        System.out.println("Do you want to do another calculation? Y/N");
        boolean doAnotherCalculation = scanner.next().equalsIgnoreCase("Y");
        if (doAnotherCalculation == true) {
            calculatorvariables();
        } else {
            System.out.println("Done! Exiting");
        }

    }
}