自定义异常不起作用

Question

我正在尝试创建两个异常，一个在月份编号大于 12 或小于 1 时抛出，另一个在月份名称无效时抛出。我以为我包含了所有必要的步骤（我不擅长例外），但我的主课仍然无法正常工作。关于我做错了什么的任何见解？

public class Month {
private int monthNumber;

/**
 * Creates a new month set to January
 */
public Month(){
    monthNumber = 1;
}

/**
 * Creates a month set to the month number provided by the user
 * @param m the number of the month
 */
public Month(int m) throws MonthsNumberException{
    if (m<1 || m>12){
       throw new MonthsNumberException("Number has to be greater than 1 and less than 12");
    }else{
        monthNumber = m;
    }
}

/**
 * Creates a month based on the string name provided
 * @param m String values for the name of the month
 */
public Month(String m) throws MonthsNameException{
    switch(m){
        case "January":
            monthNumber = 1;
            break;
        case "February":
            monthNumber = 2;
            break;
        case "March":
            monthNumber = 3;
            break;
        case "April":
            monthNumber = 4;
            break;
        case "May":
            monthNumber = 5;
            break;
        case "June":
            monthNumber = 6;
            break;
        case "July":
            monthNumber = 7;
            break;
        case "August": 
            monthNumber = 8;
            break;
        case "September":
            monthNumber = 9;
            break;
        case "October":
            monthNumber = 10;
            break;
        case "November":
            monthNumber = 11;
            break;
        case "December":
            monthNumber = 12;
            break;
                default:
    throw new MonthsNameException("Invalid month name: " + m);
    }
}

/**
 * changes the month to the number provided
 * @param m the number of the month
 */
public void setMonthNumber(int m) throws MonthsNumberException{
    if (m<1 || m>12){
        throw new MonthsNumberException("Number has to be greater than 1 and less than 12");

    }else{
        monthNumber = m;
    }
}

/**
 * returns the number of the month
 * @return the number of the month
 */
public int getMonthNumber(){
    return monthNumber;
}

/**
 * returns the name of the month
 * @return the name of the month
 */
public String getMonthName(){
    String month="";

    switch(monthNumber){
        case 1:
            month = "January";
            break;
        case 2:
            month = "February";
            break;
        case 3:
            month = "March";
            break;
        case 4:
            month = "April";
            break;
        case 5:
            month = "May";
            break;
        case 6:
            month = "June";
            break;
        case 7:
            month = "July";
            break;
        case 8:
            month = "August";
            break;
        case 9:
            month = "September";
            break;
        case 10:
            month = "October";
            break;
        case 11:
            month = "November";
            break;
        case 12:
            month = "December";
            break;

    }
    return month;
}

/**
 * returns a string representation of the month
 * @return the name of the month
 */
public String toString(){
    return getMonthName();
}

/**
 * if the two items are the same returns true
 * @param m the month object to compare
 * @return true if they are the same, false if not
 */
public boolean equals(Month m){
    if (m.getMonthNumber() == this.getMonthNumber()){
        return true;
    }else{
        return false;
    }
}

/**
 * If this calling item is after the month object passed as argument returns true
 * @param m the month object
 * @return true if calling object greater, false of argument greater
 */
public boolean greaterThan(Month m){
    if (this.getMonthNumber()>m.getMonthNumber()){
        return true;
    }else{
        return false;
    }
}

/**
 * If this calling item is before the month object passed as argument returns true
 * @param m the month object
 * @return true if calling object less than, false of argument less than
 */
public boolean lessThan(Month m){
    if (this.getMonthNumber()<m.getMonthNumber()){
        return true;
    }else{
        return false;
    }
}
class MonthsNumberException extends Exception
{
    public MonthsNumberException(String message)
    {
        super(message);
    }
}
class MonthsNameException extends Exception
{
    public MonthsNameException(String message)
    {
        super(message);
    }
}

}

import javax.swing.*;

public class MonthDemo {

/**
 * @param args the command line arguments
 */
public static void main(String[] args) {
    String response = JOptionPane.showInputDialog(null, "Please enter a month number");
    int mNumber = Integer.parseInt(response);

    Month m1 = new Month(mNumber);

    JOptionPane.showMessageDialog(null, m1.toString());

    response = JOptionPane.showInputDialog(null, "Please enter a month name");
    Month m2 = new Month(response);
    JOptionPane.showMessageDialog(null, m2.toString());

}

}

Answer 1

问题 #1：您必须在更改月份时抛出异常。

问题 #2：不允许在 Main 中捕获异常 方法。

在完全了解您的作业后，我为您提供了一个简短的解决方案。当您扩展 Exception 时，这称为“已检查”异常，这意味着您必须将其包围在 try catch 中，但是如果您扩展 RuntimeException(also Error)，它将允许您在主线程中执行该方法而无需处理它。这样做的结果是如果抛出异常，您的程序将关闭，但这似乎是您作业的预期结果。将您的代码与原始问题中的代码保持一致，然后进行更改。

@SuppressWarnings("serial")
class MonthsNumberException extends RuntimeException {
    public MonthsNumberException(String message) {
        super(message);
    }
}

@SuppressWarnings("serial")
class MonthsNameException extends RuntimeException {
    public MonthsNameException(String message) {
        super(message);
    }
}

这应该可以解决你的作业问题。

Answer 2

没有试过你的代码，因为你没有告诉我们确切的错误，我只是在这里猜测。

您提到Month m2 = new Month(response); 行有问题。

Month(int) 构造函数正在抛出一个检查异常。但是，作为此构造函数的调用者的 main 方法没有进行任何适当的处理。您应该catch 它，或者将您的主要方法声明为throws MonthsNumberException。

---

请不要像这样简单地扔掉一大段代码并“问”问题。你应该做很多事情：

1. 有一个简化的程序来验证您的理解，并展示您的问题。 lessThan 方法与问题有何关系？您应该从您的问题中删除所有这些“噪音”，以便人们可以专注于您的问题

2. 您应该提供足够的信息。如果有错误，请告诉我们错误消息或问题症状。仅仅丢掉一大段代码是没有用的。