在 Do While 循环中使用 try/Catch答案

【问题标题】：Using a try/Catch in a Do While loop在 Do While 循环中使用 try/Catch
【发布时间】：2021-11-20 03:45:15
【问题描述】：

我正在尝试在 do-while 循环中使用 try-catch 语句。逻辑似乎有效，但 do 循环不会一遍又一遍地循环。如果它进入 catch 中，它似乎只是跳出了 do 循环。

private boolean madeChoice = false;

public void whatToDo(){
    System.out.println("");
    System.out.println("");
    System.out.println("=====================================");
    System.out.println("Welcome");
    System.out.println("=====================================\n");
    System.out.println("What would you like to do today? Your choices are: \n");
    choices();

    do{
        try{
            System.out.println("");
            System.out.println("Please enter your choice");
            int numberEntered = keyboard.nextInt();

            if(numberEntered > 3 || numberEntered < 1){
                System.out.println("-----------------------------------------------------------");
                System.out.println("That is not a choice. Please choose from the following: \n");
                choices();
                numberEntered = keyboard.nextInt();
               
            }else{
                System.out.println("That is a good CHOICE");
                madeChoice = true;
            }
          
        }catch (InputMismatchException e){
            System.out.println("-----------------------------------------------------------");
            System.out.println("This is not a number. Please choose from the following: \n");
            choices();
            
        }

    }while(!madeChoice);

}

private void choices(){
    System.out.println("1. Add a new set into your account");
    System.out.println("2. See all the sets in your account");
    System.out.println("3. Exit the Account Manger.");
}

【问题讨论】：

似乎在将 madeChoice 设置为 true 之前出现错误，因此 madeChoice 保持为 false 并且循环在那里停止。也许你应该改变你处理问题的方式。真的需要 madeChoice 变量吗？您希望循环何时准确结束？编辑：您可以在 catch 子句中将 madeChoice 设置为 true 吗？
所以我在 whatToDo 方法上方将 madeChoice 设置为 false。抱歉，我应该添加那个。
你不想在!madeChoice循环吗？
我希望循环仅在用户输入 1,2 或 3 时结束。如果有其他任何情况，如果它应该被 if-else 语句捕获，或者如果它是 catch 方法中的错误。
当用户输入错误的数字时，madeChoice有什么值？该值会使循环退出还是继续？

标签： java try-catch do-while

【解决方案1】：

在continue之前添加keyboard.nextLine()，当出现异常时，需要“吃掉”输入：

           catch (InputMismatchException e){
                System.out.println("-----------------------------------------------------------");
                System.out.println("This is not a number. Please choose from the following: \n");
                choices();
                keyboard.nextLine();
                continue;
                // numberEntered = keyboard.nextInt();
            }

编辑，我修改了你的一些代码：

public void whatToDo(){
        System.out.println("");
        System.out.println("");
        System.out.println("=====================================");
        System.out.println("Welcome");
        System.out.println("=====================================\n");
        System.out.println("What would you like to do today? Your choices are: \n");
        Scanner keyboard = new Scanner(System.in);
        do{
            try{
                choices();
                System.out.println("");
                System.out.println("Please enter your choice");
                int numberEntered = keyboard.nextInt();

                if (numberEntered >= 1 && numberEntered <= 3) {
                    System.out.println("That is a good CHOICE");
                    madeChoice = true;
                } else {
                    System.out.println("-----------------------------------------------------------");
                    System.out.println("That is not a choice. Please choose from the following: \n");
                }
            }catch (InputMismatchException e){
                System.out.println("-----------------------------------------------------------");
                System.out.println("This is not a number. Please choose from the following: \n");
                keyboard.next();
                // numberEntered = keyboard.nextInt();
            }

        }while(!madeChoice);

    }

【讨论】：

成功了！但它似乎仍然卡在这里 if(numberEntered > 3 || numberEntered
我想我无法在回复中添加代码？

【解决方案2】：

也许你可以将你的代码更新为这样的东西，这似乎对我有用：

private boolean madeChoice = false;
private static boolean isMissMatchException = false ;
private static boolean isInvalidInput = false ;

public void whatToDo(){
    if(Test.isMissMatchException) 
    {
         System.out.println("-----------------------------------------------------------");
         System.out.println("This is not a number. Please choose from the following: \n");
         Test.isMissMatchException = false ;
    } else if (Test.isInvalidInput) 
    {
        System.out.println("-----------------------------------------------------------");
        System.out.println("That is not a choice. Please choose from the following: \n");
        Test.isInvalidInput = false ;
    } else {            
        System.out.println("");
        System.out.println("");
        System.out.println("=====================================");
        System.out.println("Welcome");
        System.out.println("=====================================\n");
        System.out.println("What would you like to do today? Your choices are: \n");
    }
    choices();
    
    do{
        try{
            System.out.println("");
            System.out.println("Please enter your choice");
            
            @SuppressWarnings("resource")
            int numberEntered = new Scanner(System.in).nextInt();

            if(numberEntered > 3 || numberEntered < 1){
                Test.isInvalidInput = true ;
                this.whatToDo();
               
            }else{
                System.out.println("That is a good CHOICE");
                madeChoice = true;
            }
          
        }catch (InputMismatchException e){
            Test.isMissMatchException = true ;
            this.whatToDo();
        }

    }while(madeChoice);

}

private void choices(){
    System.out.println("1. Add a new set into your account");
    System.out.println("2. See all the sets in your account");
    System.out.println("3. Exit the Account Manger.");
}

【讨论】：