Question

首先，我想说通过使用if-else配置或while循环，我知道这个程序可以更容易完成，但我想知道如何使用异常类来完成它。（我猜我需要使用try-catch块来定制异常）。

import java.util.Scanner;

class AgeChecker
{
    public static void main(String [] args)
    {
        Scanner inputdata = new Scanner(System.in);
        System.out.print("Enter your name: ");
        String name = inputdata.nextLine();
        System.out.print(name+", enter your age: ");
        int age = inputdata.nextInt();
        try
        { // age entered must be between 0-125 (how to trigger exception in catch block?)
            System.out.println("You entered: "+age);
        }
        catch(Exception e)
        {
            System.out.println("Out of range error! (must be between ages 0 and 125)"+e);
        }
        finally
        {
            System.out.println("Age Checking Complete.");
        }
    }
}

Answer 1

虽然我不确定为什么不使用if-else而不是异常，但您可以通过继承现有异常类来创建自定义异常。通常，您将为“声明的”异常子类化Exception，并为您不希望捕获的异常创建RuntimeException。在你的情况下，你可以只是子类Exception，如：

public MyException extends Exception
{
}

然后在发现范围问题时抛出它：

throw new MyException();

然后通过捕获异常来捕获它，就像你做的那样或MyException：

catch(MyException exp) ...

Answer 2

package example.stackoverflow;

import java.util.Scanner;

public class AgeChecker
{
    public static final int MIN_AGE = 0;
    public static final int MAX_AGE = 125;

    static class InvalidAgeException extends Exception
    {
        private static final long serialVersionUID = 1340715735048104509L;

        public InvalidAgeException()
        { }

        public InvalidAgeException(String message)
        {
            super(message);
        }

        public InvalidAgeException(String message, Throwable cause)
        {
            super(message, cause);
        }
    }

    public static void main(String[] args)
    {
        Scanner inputdata = new Scanner(System.in);
        System.out.print("Enter your name: ");
        String name = inputdata.nextLine();
        System.out.print(name+", enter your age: ");
        int age = inputdata.nextInt();
        try
        {
            System.out.println("You entered: "+age);
            // Assuming age limits are non-inclusive
            if( (age <= MIN_AGE) || (age >= MAX_AGE) )
            {
                throw new InvalidAgeException("Out of range error! (must be between ages 0 and 125)");
            }
        }
        catch(InvalidAgeException e)
        {
            e.printStackTrace();
        }
        finally
        {
            System.out.println("Age Checking Complete.");
            if(inputdata != null)
            {
                inputdata.close();
            }
        }
    }
}

另请注意，只要完成扫描仪，就需要关闭（）扫描仪。在finally块中进行这样的清理通常很有用，所以我把它放在这个例子中。

Answer 3

您可以创建自己的Exception实例。如果您想触发catch阻止，则需要throw中的Exception try：

try {
    System.out.println("Enter your age: ");
    int age = scanner.nextInt();
    if(isInvalid(age)) {
        throw new Exception("Age is invalid!");
    }
} catch (Exception e) {
    // etc
}

您可能还需要考虑subclassing Exception提供一些bit more information来解决导致问题的原因。

Answer 4

public class yourExcetionActivity extends Exception 
{
    public yourExcetionActivity() { }
    public yourExcetionActivity(String string) {
        super(string);
    }
}

我如何定制例外？

4 个答案: