为什么要用三个不同的对话框来输入东西来惹恼用户,为什么不在一个对话框中一次性完成所有这些并节省时间,而不是测试用户的耐心呢?
您可以在单个对话框中添加所有内容,方法是将所有字段放在您的JPanel,然后将其添加JPanel到您的JOptionPane. 下面的代码可以澄清一点:
import java.awt.*;
import java.util.*;
import javax.swing.*;
public class AverageExample
{
    private double[] marks;
    private JTextField[] marksField;
    private JLabel resultLabel;
    public AverageExample()
    {
        marks = new double[3];
        marksField = new JTextField[3];
        marksField[0] = new JTextField(10);
        marksField[1] = new JTextField(10);
        marksField[2] = new JTextField(10);
    }
    private void displayGUI()
    {
        int selection = JOptionPane.showConfirmDialog(
                null, getPanel(), "Input Form : "
                                , JOptionPane.OK_CANCEL_OPTION
                                , JOptionPane.PLAIN_MESSAGE);
        if (selection == JOptionPane.OK_OPTION) 
        {
            for ( int i = 0; i < 3; i++)
            {
                marks[i] = Double.valueOf(marksField[i].getText());             
            }
            Arrays.sort(marks);
            double average = (marks[1] + marks[2]) / 2.0;
            JOptionPane.showMessageDialog(null
                    , "Average is : " + Double.toString(average)
                    , "Average : "
                    , JOptionPane.PLAIN_MESSAGE);
        }
        else if (selection == JOptionPane.CANCEL_OPTION)
        {
            // Do something here.
        }
    }
    private JPanel getPanel()
    {
        JPanel basePanel = new JPanel();
        //basePanel.setLayout(new BorderLayout(5, 5));
        basePanel.setOpaque(true);
        basePanel.setBackground(Color.BLUE.darker());
        JPanel centerPanel = new JPanel();
        centerPanel.setLayout(new GridLayout(3, 2, 5, 5));
        centerPanel.setBorder(
            BorderFactory.createEmptyBorder(5, 5, 5, 5));
        centerPanel.setOpaque(true);
        centerPanel.setBackground(Color.WHITE);
        JLabel mLabel1 = new JLabel("Enter Marks 1 : ");
        JLabel mLabel2 = new JLabel("Enter Marks 2 : ");
        JLabel mLabel3 = new JLabel("Enter Marks 3 : ");
        centerPanel.add(mLabel1);
        centerPanel.add(marksField[0]);
        centerPanel.add(mLabel2);
        centerPanel.add(marksField[1]);
        centerPanel.add(mLabel3);
        centerPanel.add(marksField[2]);
        basePanel.add(centerPanel);
        return basePanel;
    }
    public static void main(String... args)
    {
        SwingUtilities.invokeLater(new Runnable()
        {
            @Override
            public void run()
            {
                new AverageExample().displayGUI();
            }
        });
    }
}