java - 使用 JOPtionPane 时遇到问题

Question

我是 Java 初学者，我在解决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。然而，我的困难来自这样的事实: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。另外，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置在文本字段中。

从程序的其他部分退出也会在主线程中产生异常，因此我希望能够捕获这些异常并正常退出而不是出错。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。输入对话框的图标也是如此。我不希望它们显示，但程序无法编译，并且如果我将它们放入输入对话框中，则显示找不到符号。不过它适用于选项对话框。

以上是问题解决之前

非常感谢那些花时间阅读本文的人。

以下是代码(请注意，investment1 和investment2 只是具有正确公式的简单静态方法):

编辑以下代码；只是尝试添加空字符串错误检查

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);
}  

Answer 1

如果用户单击“x”关闭按钮JOptionPane将返回JOptionPane.CLOSED_OPTION

您应该首先检查此...

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

您还应该注意，按照您的方式使用 JOptionPane.showOptionDialog，JOptionPane 将返回用户所选选项的索引。

这意味着返回值 0 表示用户选择了“计算达到目标的年数” 并且返回值 1表示用户选择了“计算给定年数的目标”

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

已更新示例

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

                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);
    }

更新了额外的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，我只需将 again 设置为等于 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);
}