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我是 Java 的初学者，但遇到问题时遇到了一些困难。我正在使用 JOPtionPane 向用户询问一些问题。但是，我的困难来自这样一个事实，即当用户单击 X 或取消程序中的任何位置时，我不知道如何正确处理异常。此外，当我查看 Java API 并了解如何实现标题时，我尝试了它，但现在应该将标题放在文本字段中。

从程序的其他部分退出也会在主线程中产生异常，所以我希望能够捕获这些异常并优雅地退出而不是出错。此外，在输入对话框中，标题“投资顾问”显示在文本字段内。我查看了 API，似乎我使用了正确的形式，但显然不是。与输入对话框的图标相同。我不希望它们显示，但是如果我将它们放在输入对话框中，程序不会编译并说找不到符号。它适用于选项对话框。

以上来自问题解决之前

非常感谢那些花时间阅读本文的人。

这是代码（注意invest1 和invest2 只是简单的静态方法和正确的公式）：

编辑以下代码；只是尝试添加错误检查空字符串

public static void main(String[] args) 
{  
String initialAmt_Str, targetAmt_Str, interestPct_Str, years_Str, result;
double principle = 0, target = 0, interest = 0;
int again = JOptionPane.NO_OPTION, time = 0;

NumberFormat fmt = NumberFormat.getCurrencyInstance();

do {  
     Object[] options = {"Compute years to reach target amount",
        "Compute target amount given number of years"};

     int choice = JOptionPane.showOptionDialog(null, "Please choose what you would like to do.",
            "Investment Advisor", JOptionPane.YES_NO_OPTION,
            JOptionPane.PLAIN_MESSAGE, null, options, null);

     if (choice != JOptionPane.CANCEL_OPTION) 
     {

        if (choice == 1) 
        {        
           initialAmt_Str = JOptionPane.showInputDialog (null, "Enter the principle:", "Investment Advisor", 
           JOptionPane.PLAIN_MESSAGE);

           if (initialAmt_Str != null) 
              principle = Double.parseDouble(initialAmt_Str);

           else 
              System.exit(0);


           interestPct_Str = JOptionPane.showInputDialog (null, "Enter the interest rate as a"
                        + " percentage (without the percent sign):", "Investment Advisor", JOptionPane.PLAIN_MESSAGE); 

           if (interestPct_Str != null) 
              interest = Double.parseDouble(interestPct_Str);

           else 
              System.exit(0); 


           years_Str = JOptionPane.showInputDialog (null, "Enter the amount of years:", "Investment Advisor", 
           JOptionPane.PLAIN_MESSAGE);

           if (years_Str != null) 
              time = Integer.parseInt(years_Str);

           else 
              System.exit(0);  

           result = "Your target amount given the number of years is " + 
              fmt.format(investment2(principle, interest, time)) + ".";

           JOptionPane.showMessageDialog (null, result, "Investment Advisor", JOptionPane.PLAIN_MESSAGE);

           again = JOptionPane.YES_OPTION;
        }
     }

     else 
        again = JOptionPane.NO_OPTION;


     if (choice == 0) 
     {
        initialAmt_Str = JOptionPane.showInputDialog (null,"Enter the principle:","Investment Advisor",
        JOptionPane.PLAIN_MESSAGE);

        if (initialAmt_Str != null) 
           principle = Double.parseDouble(initialAmt_Str);

        else 
           System.exit(0);


        interestPct_Str = JOptionPane.showInputDialog (null, "Enter the interest rate as a"
                        + " percentage (without the percent sign):", "Investment Advisor", JOptionPane.PLAIN_MESSAGE); 

        if (interestPct_Str != null) 
           interest = Double.parseDouble(interestPct_Str);

        else 
           System.exit(0); 


        targetAmt_Str = JOptionPane.showInputDialog (null, "Enter your target amount:", "Investment Advisor", 
        JOptionPane.PLAIN_MESSAGE);


        if (targetAmt_Str != null)
           target = Double.parseDouble(targetAmt_Str);

        else
           System.exit(0);

        result = "You will reach your target amount in " + 
              investment1(principle, target, interest) + 
              (investment1(principle, target, interest) == 1 ? " year." : " years.");

        JOptionPane.showMessageDialog (null, result, "Investment Advisor", JOptionPane.PLAIN_MESSAGE);

        again = JOptionPane.YES_OPTION;

     }

     if (again != JOptionPane.NO_OPTION) 
        again = JOptionPane.showConfirmDialog(null, "Find Another?", "", JOptionPane.YES_NO_OPTION, 
        JOptionPane.PLAIN_MESSAGE); 

} while (again == JOptionPane.YES_OPTION);
}
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1 回答 1

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如果用户点击“x”关闭按钮JOptionPane将返回JOptionPane.CLOSED_OPTION

你应该从检查这个开始......

if (choice != JOptionPane.CLOSED_OPTION) {
    // Do the normal stuff
} else {
    // Break out of the do loop
    break;
}

您还应该注意，使用JOptionPane.showOptionDialog您拥有的方式，JOptionPane将返回用户选择的选项的索引。

这意味着返回值0表示用户选择"Compute years to reach target"，返回值1表示用户选择"Compute target given number of years"

使用JOptionPane.NO_OPTION或JOptionPane.YES_OPTION可能无法获得您期望的结果......

更新了示例

您的重组允许一个稍微“偷偷摸摸”的选项，而不是使用中断，我简单地将again变量设置为JOptionPane.NO_OPTION当用户关闭选项对话框时......

public static void main(String[] args) {
        String initialAmt_Str, targetAmt_Str, interestPct_Str, years_Str, result;
        double principle, target, interest;
        int again, time;

        NumberFormat fmt = NumberFormat.getCurrencyInstance();

        do {
            Object[] options = {"Compute years to reach target",
                "Compute target given number of years"};

            int choice = JOptionPane.showOptionDialog(null, "Please choose what you would like to do.",
                    "Investment Advisor", JOptionPane.YES_NO_OPTION,
                    JOptionPane.PLAIN_MESSAGE, null, options, null);

            if (choice != JOptionPane.CANCEL_OPTION) {

                if (choice == 1) {
                    JOptionPane.showMessageDialog(null, "Compute target given number of years");
                } else if (choice == 0) {
                    JOptionPane.showMessageDialog(null, "Compute years to reach target");
                }

                again = JOptionPane.showConfirmDialog(null, "Find Another?");

            } else {
                again = JOptionPane.NO_OPTION;
            }
        } while (again == JOptionPane.YES_OPTION);
    }

更新了附加示例以处理取消的输入

因此，如果用户单击输入对话框上的“x”按钮，他们将返回null. 此时，您需要检查null结果并选择如何处理它。在下面的示例中，我只是again将JOptionPane.NO_OPTION

public static void main(String[] args) {
    String initialAmt_Str, targetAmt_Str, interestPct_Str, years_Str, result;
    double principle, target, interest;
    int again, time;

    NumberFormat fmt = NumberFormat.getCurrencyInstance();

    do {
        Object[] options = {"Compute years to reach target",
            "Compute target given number of years"};

        int choice = JOptionPane.showOptionDialog(null, "Please choose what you would like to do.",
                "Investment Advisor", JOptionPane.YES_NO_OPTION,
                JOptionPane.PLAIN_MESSAGE, null, options, null);

        if (choice != JOptionPane.CANCEL_OPTION) {

            again = JOptionPane.YES_OPTION;
            if (choice == 1) {
                String input = JOptionPane.showInputDialog("Enter the principle:", "Investment Advisor");
                if (input != null) {
                    // Process further...
                    System.out.println("Continue processing...");
                } else {
                    again = JOptionPane.NO_OPTION;
                }
            } else if (choice == 0) {
                String input = JOptionPane.showInputDialog("Enter your target amount:", "Investment Advisor");
                if (input != null) {
                    // Process further...
                    System.out.println("Continue processing...");
                } else {
                    again = JOptionPane.NO_OPTION;
                }
            }

            if (again != JOptionPane.NO_OPTION) {
                again = JOptionPane.showConfirmDialog(null, "Find Another?");
            }

        } else {
            again = JOptionPane.NO_OPTION;
        }
    } while (again == JOptionPane.YES_OPTION);
}
于 2013-11-11T01:38:42.127 回答