测试 NFE 的 Catch 语句 [英] Testing Catch Statements of a NFE

问题描述

好的，所以我是编程课程的入门学生，我正在尝试测试 NFE 的 catch 语句.我不知道如何正确格式化代码，但在这里.

Alright so I am an intro student in a programming class and I am trying to test a catch statement of a NFE. I don't know how to format the code properly, but here it is.

import java.util.Scanner;

public class Geo {

    public static void main(String[] args) {

        try {
            Scanner inp = new Scanner(System.in);
            System.out.print("Name?");
            String name = inp.nextLine();
            System.out.print("Number?");
            double num = inp.nextDouble();
            System.out.print("Integer?");
            int num2 = inp.nextInt();
        } catch(NumberFormatException e) {
            System.out.println("Usage error");
        }
        System.out.println(name);
        System.out.println(num);
        System.out.println(num2);   
    }

}

它一直说变量，name，num 和 num2 是未定义的.我在这里做错了什么，因为我正在回顾一个旧实验室，这正是我以前所做的.有什么提示吗?

It keeps saying the variables, name, num, and num2 are undefined. What am I doing wrong here, because I was looking back at an old lab and that is exactly how I had done it before. Any hints?

现在我修复了它，代码看起来像这样

Now I fixed it so the code looks like this

public static void main(String[] args) {

public static void main(String[] args) {

        try {
            Scanner inp = new Scanner(System.in);
            System.out.print("Name?");
            String name = inp.nextLine();
            System.out.print("Number?");
            double num = inp.nextDouble();
            System.out.print("Integer?");
            int num2 = inp.nextInt();
            System.out.println(name);
            System.out.println(num);
            System.out.println(num2);
        } catch(NumberFormatException e) {
            System.out.println("Usage error");
        }

    }

但是捕获没有运行.这怎么解决.就像我希望它完全运行 try 一样，但如果出现问题，它会继续运行，然后尝试退出，然后发现问题.

but the catch isnt running. How does that get fixed. Like I want it run the try completely, but if something is wrong it keeps running, then out of try, then catches the issue.

推荐答案

你必须在 try/catch 之上初始化变量.

You must initial variables on top of try/catch.

public static void main(String[] args) {
    String name = null;
    double num = 0;
    int num2 = 0;
    try {
        Scanner inp = new Scanner(System.in);
        System.out.print("Name?");
        name = inp.nextLine();
        System.out.print("Number?");
        num = inp.nextDouble();
        System.out.print("Integer?");
        num2 = inp.nextInt();
    } catch (Exception e) {
        System.out.println("Usage error");
    }
    System.out.println(name);
    System.out.println(num);
    System.out.println(num2);
}

或

public static void main(String[] args) {
    try {
        Scanner inp = new Scanner(System.in);
        System.out.print("Name?");
        String name = inp.nextLine();
        System.out.print("Number?");
        double num = inp.nextDouble();
        System.out.print("Integer?");
        int num2 = inp.nextInt();

        System.out.println(name);
        System.out.println(num);
        System.out.println(num2);
    } catch (Exception e) {
        System.out.println("Usage error");
    }
}

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