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Java Swing - 如何默认情况下选择JDesktopPane上的InternalFrame

jframe 【jframe】
我们想知道如何默认情况下选择JDesktopPane上的InternalFrame。
代码展示 运行结果 
import java.awt.BorderLayout;
import java.awt.Component;
import java.awt.HeadlessException;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

import javax.swing.JDesktopPane;
import javax.swing.JFrame;
import javax.swing.JInternalFrame;

public class Main extends JFrame {
  private Internal internalFrame;

  public Main() throws HeadlessException {
    setBounds(10, 10, 600, 400);
    setDefaultCloseOperation(EXIT_ON_CLOSE);
    setLayout(new BorderLayout());
    add(createDesktop(), BorderLayout.CENTER);
    addWindowListener(new WindowAdapter() {
      public void windowOpened(WindowEvent e) {
        internalFrame.setVisible(true);
      }
    });
    setVisible(true);
  }
  private Component createDesktop() {
    JDesktopPane d = new JDesktopPane();
    internalFrame = new Internal("first");
    d.add(internalFrame);
    return d;
  }
  public static void main(String[] a) {
    new Main();
  }
}
class Internal extends JInternalFrame {
  public Internal(String title) {
    super(title);
    setBounds(10, 10, 300, 100);
  }
}