Using JDK on Solaris, if you create a java.awt.Window
you can get a NPE and the window fails to be displayed
unless you explicitly reshape the window before displaying it, to
give it non-zero dimensions.

This was observed with JDK1.1.4 on Solaris 2.6, but is not limited to
that combination.

You get no clue what happened under java - just no window appears

Running under java_g you would see the following

% java_g ShowWindow
Xt error
Exception occurred during event dispatching:
java.lang.NullPointerException
        at sun.awt.motif.MComponentPeer.<init>(MComponentPeer.java:106)
        at sun.awt.motif.MCanvasPeer.<init>(MCanvasPeer.java:35)
        at sun.awt.motif.MPanelPeer.<init>(MPanelPeer.java:29)
        at sun.awt.motif.MWindowPeer.<init>(MWindowPeer.java:42)
        at sun.awt.motif.MToolkit.createWindow(MToolkit.java:140)
        at java.awt.Window.addNotify(Window.java:106)
        at java.awt.Window.pack(Window.java:122)
        at ShowWindow.actionPerformed(ShowWindow.java:28)
        at java.awt.Button.processActionEvent(Button.java:254)
        at java.awt.Button.processEvent(Button.java:227)
        at java.awt.Component.dispatchEventImpl(Component.java:1764)
        at java.awt.Component.dispatchEvent(Component.java:1704)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:63)

At a Java application code level we
1) create a window
2) add a child component
3) display the window

Internally when we do the last step, the AWT creates peer objects
and the Motif pop up shell via "XtCreatePopupShell"

When this happens Xt generates an error, since the child component
has not been used to define an initial size for the window , and
so the values passed in are both zero.

Xt explicitly barfs at this, generating an Xt error.

In libXt/Intrinsic.h, the Realize() method has a check:

        if (wid->core.width == 0 || wid->core.height == 0) {
            Cardinal count = 1;
            XtErrorMsg("invalidDimension", "shellRealize", XtCXtToolkitError,
                       "Shell widget %s has zero width and/or height",
                       &wid->core.name, &count);
        }

JDK's installed xtError() handler emits the concise "Xt Error" message
if running under java_g. The default Xt error concerning invalid
dimensions would have been more clear.

The problem occurs in src/solaris/sun/awt_Window.c

java test case herewith
// ShowWindow.java

import java.awt.*;
import java.awt.event.*;

class ShowWindow extends Frame implements ActionListener, WindowListener {

  public static void main(String args[]) {
    ShowWindow w = new ShowWindow();
    w.setVisible(true);
  }

  public ShowWindow() {
    super("ShowWindow");
    setLayout(new FlowLayout());
    add(showButton = new Button("Show"));
    add(hideButton = new Button("Hide"));
    showButton.addActionListener(this);
    hideButton.addActionListener(this);

    win = new Window(this);
    win.add("Center", new Label("Hello World"));
    addWindowListener(this);
    pack();
  }

  public void actionPerformed(ActionEvent e) {
    if (e.getSource() == showButton) {
        //win.reshape(400,200,100,100);
        win.pack();
        win.setVisible(true);
    }
    else if (e.getSource() == hideButton)
        win.setVisible(false);
 }
 

 public void windowOpened(WindowEvent e) {
 }

 public void windowClosing(WindowEvent e) {
   System.exit(0);
 }

 public void windowClosed(WindowEvent e) {
 }

 public void windowIconified(WindowEvent e) {
 }

 public void windowDeiconified(WindowEvent e) {
 }

 public void windowActivated(WindowEvent e) {
 }

 public void windowDeactivated(WindowEvent e) {
 }


 private Window win;
 private Button showButton;
 private Button hideButton;

}