A JInternalFrame created by using the constructor
JInternalFrame(String, true, true, true, true)
is not iconifiable.

The following application demonstrates this.

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/*
 * JInternalFrameBug.java
 * An internal frame created by using the constructor
 * JInternalFrame(String, true, true, true, true) is
 * not iconifiable
 *
 */

import com.sun.java.swing.*;
import java.awt.Color;
import java.awt.BorderLayout;
import java.awt.GridLayout;
import java.awt.event.*;

public class JInternalFrameBug extends JPanel {
   JInternalFrame internalFrame = new JInternalFrame("Internal Frame", true, true, true, true);

   public static void main( String[] argv ) {
     new JInternalFrameBug();
   }

   public JInternalFrameBug() {
      JFrame frame = new JFrame("JInternalFrame Test");
      JPanel infoPanel = new JPanel();
      JDesktopPane dpane = new JDesktopPane();

      frame.setLayout(new BorderLayout());
      frame.setBackground(Color.white);
      dpane.setOpaque(true);
      dpane.setBackground(Color.pink);
      internalFrame.setBackground(Color.blue);
      internalFrame.setBounds(150, 10, 200, 250);
      dpane.add(internalFrame, JLayeredPane.PALETTE_LAYER);
      dpane.validate();
      dpane.repaint();

      infoPanel.setLayout(new GridLayout(0,1));
      infoPanel.add(new JLabel("new JInternalFrame(\"Internal Frame\", true, true, true, true)"));
      infoPanel.add(new JLabel("Should be resizable, closable, maximizable, and iconfiable."));
      frame.add(BorderLayout.NORTH, infoPanel);
      frame.add(BorderLayout.CENTER, dpane);

      frame.addWindowListener(new WindowAdapter() {
             public void windowClosing(WindowEvent e) {System.exit(0);}
             public void windowClosed(WindowEvent e) {System.exit(0);}
      });

      frame.pack();
      frame.setSize(500, 400);
      frame.setVisible(true);
   }
}
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