模态 JDialog 避免卡住的最佳位置

You can add a FocusListener to your JDialog and on focusGained(...) method, you can use setLocationRelativeTo(null) for both the JFrame and the JDialog, so that they both come to the center of the screen no matter where they are before.

import java.awt.*;
import java.awt.event.FocusEvent;
import java.awt.event.FocusListener;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.*;

/**
 * Created with IntelliJ IDEA.
 * User: Gagandeep Bali
 * Date: 1/14/13
 * Time: 7:34 PM
 * To change this template use File | Settings | File Templates.
 */
public class FrameFocus
{
    private JFrame mainwindow;
    private CustomDialog customDialog;

    private void displayGUI()
    {
        mainwindow = new JFrame("Frame Focus Window Example");
        customDialog = new CustomDialog(mainwindow, "Modal Dialog", true);
        mainwindow.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);

        JPanel contentPane = new JPanel();
        JButton mainButton = new JButton(
                "Click me to open a MODAL Dialog");
        mainButton.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                if (!customDialog.isShowing())
                    customDialog.setVisible(true);
            }
        });
        contentPane.add(mainButton);
        mainwindow.setContentPane(contentPane);
        mainwindow.pack();
        mainwindow.setLocationByPlatform(true);
        mainwindow.setVisible(true);
    }

    public static void main(String... args)
    {
        EventQueue.invokeLater(new Runnable()
        {
            @Override
            public void run()
            {
                new FrameFocus().displayGUI();
            }
        });
    }
}


class CustomDialog extends JDialog
{
    private JFrame mainWindow;
    public CustomDialog(JFrame owner, String title, boolean modal)
    {
        super(owner, title, modal);
        mainWindow = owner;
        JPanel contentPane = new JPanel();
        JLabel dialogLabel = new JLabel(
                "I am a Label on JDialog.", JLabel.CENTER);
        contentPane.add(dialogLabel);
        setContentPane(contentPane);
        pack();

        addFocusListener(new FocusListener() {
            @Override
            public void focusGained(FocusEvent e) {
                mainWindow.setLocationRelativeTo(null);
                setLocationRelativeTo(null);
            }

            @Override
            public void focusLost(FocusEvent e) {
                /*
                 * Nothing written for this part yet
                 */
            }
        });
    }
}

编辑 2:

我在这里和那里搜索了一下，在我看来，实际上，您的应用程序首先出现在哪个 Monitor Screen 上，将确定它是 GraphicsConfiguration.虽然当我在 API 中漫游时，对于上述 GraphicsConfiguration 事物只有一个 getter 方法，而没有相同的 setter 方法(您仍然可以通过任何顶级窗口的构造函数指定一个，即 JFrame(...)/JDialog(...)).

GraphicsEnvironment ge = GraphicsEnvironment.
    getLocalGraphicsEnvironment();
GraphicsDevice[] gs = ge.getScreenDevices();
for (int j = 0; j < gs.length; j++) {
    GraphicsDevice gd = gs[j];
    GraphicsConfiguration[] gc =
            gd.getConfigurations();
    for (int i=0; i < gc.length; i++) {
        JFrame f = new
        JFrame(gs[j].getDefaultConfiguration());
        Canvas c = new Canvas(gc[i]);
        Rectangle gcBounds = gc[i].getBounds();
        int xoffs = gcBounds.x;
        int yoffs = gcBounds.y;
        f.getContentPane().add(c);
        f.setLocation((i*50)+xoffs, (i*60)+yoffs);
        f.show();
    }
}

int x = loc.getX() + (mainWindow.getWidth() - getWidth()) / 2;
int y = loc.getY() + (mainWindow.getHeight() - getHeight()) / 2;
setLocation(x, y);

setLocationRelativeTo(mainWindow);

class CustomDialog extends JDialog
{
    private JFrame mainWindow;
    public CustomDialog(JFrame owner, String title, boolean modal)
    {
        super(owner, title, modal);
        mainWindow = owner;
        JPanel contentPane = new JPanel();
        JLabel dialogLabel = new JLabel(
                "I am a Label on JDialog.", JLabel.CENTER);
        contentPane.add(dialogLabel);
        setContentPane(contentPane);
        pack();

        addFocusListener(new FocusListener() {
            @Override
            public void focusGained(FocusEvent e) {
                //mainWindow.setLocationRelativeTo(null);
                //setLocationRelativeTo(null);
                GraphicsEnvironment ge = GraphicsEnvironment.getLocalGraphicsEnvironment();
                GraphicsDevice[] gs = ge.getScreenDevices();
                for (int j = 0; j < gs.length; j++) {
                    GraphicsDevice gd = gs[j];
                    GraphicsConfiguration[] gc = gd.getConfigurations();
                    for (int i=0; i < gc.length; i++) {
                        Rectangle gcBounds = gc[i].getBounds();

                        Point loc = mainWindow.getLocationOnScreen();
                        if (gcBounds.contains(loc)) {
                            System.out.println("at " + j + " screen");

                            int x = gcBounds.x + (gcBounds.width - mainWindow.getWidth()) / 2;
                            int y = gcBounds.y + (gcBounds.height - mainWindow.getHeight()) / 2;
                            mainWindow.setLocation(x, y);

                            //x = (int) (loc.getX() + (mainWindow.getWidth() - CustomDialog.this.getWidth()) / 2);
                            //y = (int) (loc.getY() + (mainWindow.getHeight() - CustomDialog.this.getHeight()) / 2);
                            //CustomDialog.this.setLocation(x, y);
                            CustomDialog.this.setLocationRelativeTo(mainWindow);

                            break;
                        }
                    }
                }
            }

            @Override
            public void focusLost(FocusEvent e) {
                /*
                 * Nothing written for this part yet
                 */
            }
        });
    }
}