我不知道如何在 JAVA 中正确使用 "try"

Question

我必须处理 "application" 上的错误 "InputMismatchException"，它根据用户输入的运算符计算数字。我在我的鳕鱼中使用 "try" 但之后我的操作 "gather, reduction, division, multiplication" 不再起作用。如果用户输入一个数字，例如当他必须输入一个运算符并处理错误时，我应该在我的代码中的什么地方使用这个 "try"，而不是让我的构建失败并继续询问用户他想做什么。

package t3;

import java.util.InputMismatchException;
import java.util.Scanner;

public class T3 {


public static void main(String[] args) {
    String answer;
    do{

    Scanner ab = new Scanner(System.in);
    System.out.println("Input what operation do you want to do!");
    System.out.println("For gather: \"+\"");
    System.out.println("For reduction: \"-\"");
    System.out.println("For division: \"/\"");
    System.out.println("For multiplication: \"*\"");
    System.out.print(":");

    String operation = ab.nextLine();


    try{
    System.out.print("Input first number: ");
    int nr1 = ab.nextInt();
    System.out.print("Input second number: ");
    int nr2 = ab.nextInt();

    int gather, reduction, division, multiplication;
    gather=nr1+nr2;
    reduction=nr1-nr2;
    division=nr1/nr2;
    multiplication=nr1*nr2;
    }
    catch (InputMismatchException e)
    { System.out.println(" ------------------------------ You have to choose an operation ------------------------------"); }
    switch (operation){
        case "+" : System.out.println("The result is: " +gather);
        break;
        case "-" : System.out.println("The result is: " +reduction);
        break;
        case "/" : System.out.println("The result is: " +division);
        break;
        case "*" : System.out.println("The result is: " +multiplication);
        break;
        default : System.out.println(" !!!! You haven't chosen an operation...  \n **** Input smth like: \n+ -> gather\n- -> reduction\n/ -> division\n* -> multiplication");  
    } 

                System.out.println("Do you keep going? Yes/ No");
                Scanner tx = new Scanner(System.in);
                answer= tx.nextLine();
    }

    while(answer.equalsIgnoreCase("Yes"));
}
}

编辑：在我使用 "try" 之后，如果我输入正常输入，它会给我这个错误： Exception in thread "main" java.lang.RuntimeException: Uncompilable source code - Erroneous tree type: <any> at tema2.Tema2.main(Tema2.java:104) C:\Users\VALENTIN-CLAUDIUCOST\AppData\Local\NetBeans\Cache.3\executor-snippets\run.xml:111: The following error occurred while executing this line: C:\Users\VALENTIN-CLAUDIUCOST\AppData\Local\NetBeans\Cache.3\executor-snippets\run.xml:94: Java returned: 1 BUILD FAILED (total time: 2 seconds)

Answer 1

import java.util.InputMismatchException;
import java.util.Scanner;

public class T3 {

    public static void main(String[] args) {
        String answer;
        do {

            Scanner ab = new Scanner(System.in);
            System.out.println("Input what operation do you want to do!");
            System.out.println("For gather: \"+\"");
            System.out.println("For reduction: \"-\"");
            System.out.println("For division: \"/\"");
            System.out.println("For multiplication: \"*\"");
            System.out.print(":");

            String operation = ab.nextLine();


            try {
                System.out.print("Input first number: ");
                int nr1 = ab.nextInt();
                System.out.print("Input second number: ");
                int nr2 = ab.nextInt();

                int gather, reduction, division, multiplication;
                gather = nr1 + nr2;
                reduction = nr1 - nr2;
                division = nr1 / nr2;
                multiplication = nr1 * nr2;
                switch (operation) {
                    case "+":
                        System.out.println("The result is: " + gather);
                        break;
                    case "-":
                        System.out.println("The result is: " + reduction);
                        break;
                    case "/":
                        System.out.println("The result is: " + division);
                        break;
                    case "*":
                        System.out.println("The result is: " + multiplication);
                        break;
                    default:
                        System.out.println(" !!!! You haven't chosen an operation...  \n **** Input smth like: \n+ -> gather\n- -> reduction\n/ -> division\n* -> multiplication");
                }
            } catch (InputMismatchException e) {
                System.out.println(" ------------------------------ You have to choose an operation ------------------------------");
            }


            System.out.println("Do you keep going? Yes/ No");
            Scanner tx = new Scanner(System.in);
            answer = tx.nextLine();
        }

        while (answer.equalsIgnoreCase("Yes"));
    }
}

修复了代码格式问题，因为它需要访问在其中声明的变量，所以需要在 try 块中移位 switch。

我不知道如何在 JAVA 中正确使用 "try"

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