WindowBuilder encountered unexpected internal error #1508

C4J · 2026-05-13T10:56:05Z

C4J
May 13, 2026

I have a JFrame which does not seem to render within WindowBuilder, but runs fine. I have a rather cryptic error message and I don't know how to narrow down the specific code which is triggering the problem.

Internal Error

WindowBuilder encountered unexpected internal error.

This could be caused by a WindowBuilder bug or by a misconfiguration issue, conflict, partial update, etc.

java.lang.NullPointerException: Cannot invoke "org.eclipse.wb.internal.core.editor.structure.components.IComponentsTree.getContentProvider()" because "this.m_componentsTree" is null

Hide stack trace.
Stack trace:

java.lang.NullPointerException: Cannot invoke "org.eclipse.wb.internal.core.editor.structure.components.IComponentsTree.getContentProvider()" because "this.m_componentsTree" is null
at org.eclipse.wb.internal.core.editor.UndoManager.setRoot(UndoManager.java:157)
at org.eclipse.wb.internal.core.editor.DesignPage.internal_refreshGEF(DesignPage.java:589)
at org.eclipse.wb.internal.core.editor.DesignPage$8.run(DesignPage.java:456)
at org.eclipse.jface.operation.ModalContext$ModalContextThread.run(ModalContext.java:123)
Full context stack trace:

java.lang.NullPointerException: Cannot invoke "org.eclipse.wb.internal.core.editor.structure.components.IComponentsTree.getContentProvider()" because "this.m_componentsTree" is null
at org.eclipse.wb.internal.core.editor.UndoManager.setRoot(UndoManager.java:157)
at org.eclipse.wb.internal.core.editor.DesignPage.internal_refreshGEF(DesignPage.java:589)
at org.eclipse.wb.internal.core.editor.DesignPage$8.run(DesignPage.java:456)
at org.eclipse.jface.operation.ModalContext$ModalContextThread.run(ModalContext.java:123)

<<<<<<<<<<<<***************>>>>>>>>>>>>>>>

!SESSION 2026-05-13 11:06:27.209 -----------------------------------------------
eclipse.buildId=4.40.0.20260430-0612
java.version=21.0.10
java.vendor=Eclipse Adoptium
BootLoader constants: OS=macosx, ARCH=aarch64, WS=cocoa, NL=en_GB
Framework arguments: -product org.eclipse.epp.package.jee.product -keyring /Users/dave/.eclipse_keyring
Command-line arguments: -os macosx -ws cocoa -arch aarch64 -product org.eclipse.epp.package.jee.product -keyring /Users/dave/.eclipse_keyring

This is a continuation of log file /Users/dave/Commander4j/Source/b8/Scratchpad/.metadata/.bak_0.log
Created Time: 2026-05-13 11:45:21.767

!ENTRY org.eclipse.wb.core 4 4 2026-05-13 11:45:21.768
!MESSAGE Designer [1.24.0.202605051923.202605131107]: Cannot invoke "org.eclipse.wb.internal.core.editor.structure.components.IComponentsTree.getContentProvider()" because "this.m_componentsTree" is null
!STACK 0
java.lang.NullPointerException: Cannot invoke "org.eclipse.wb.internal.core.editor.structure.components.IComponentsTree.getContentProvider()" because "this.m_componentsTree" is null
at org.eclipse.wb.internal.core.editor.UndoManager.setRoot(UndoManager.java:157)
at org.eclipse.wb.internal.core.editor.DesignPage.internal_refreshGEF(DesignPage.java:589)
at org.eclipse.wb.internal.core.editor.DesignPage$8.run(DesignPage.java:456)
at org.eclipse.jface.operation.ModalContext$ModalContextThread.run(ModalContext.java:123)

<<<<<<<<<<<<***************>>>>>>>>>>>>>>>

eclipse.buildId=4.40.0.20260430-0612
java.version=21.0.10
java.vendor=Eclipse Adoptium
BootLoader constants: OS=macosx, ARCH=aarch64, WS=cocoa, NL=en_GB
Framework arguments: -product org.eclipse.epp.package.jee.product -keyring /Users/dave/.eclipse_keyring
Command-line arguments: -os macosx -ws cocoa -arch aarch64 -product org.eclipse.epp.package.jee.product -keyring /Users/dave/.eclipse_keyring

org.eclipse.ui
Error
Wed May 13 11:45:21 BST 2026
Unhandled event loop exception

java.lang.NullPointerException: Cannot read field "x" because "o" is null
at org.eclipse.wb.internal.swing.model.CoordinateUtils.get(CoordinateUtils.java:49)
at org.eclipse.wb.internal.swing.model.component.JTabbedPaneInfo.getTabs(JTabbedPaneInfo.java:113)
at org.eclipse.wb.internal.swing.gef.part.JTabbedPaneEditPart.getModelChildren(JTabbedPaneEditPart.java:65)
at org.eclipse.wb.gef.core.EditPart.refreshChildren(EditPart.java:101)
at org.eclipse.wb.gef.core.EditPart.refresh(EditPart.java:80)
at org.eclipse.wb.core.gef.part.AbstractComponentEditPart.refresh(AbstractComponentEditPart.java:203)
at org.eclipse.gef.editparts.AbstractEditPart.addNotify(AbstractEditPart.java:260)
at org.eclipse.gef.editparts.AbstractEditPart.addChild(AbstractEditPart.java:221)
at org.eclipse.wb.gef.core.EditPart.refreshChildren(EditPart.java:120)
at org.eclipse.wb.gef.core.EditPart.refresh(EditPart.java:80)
at org.eclipse.wb.core.gef.part.AbstractComponentEditPart.refresh(AbstractComponentEditPart.java:203)
at org.eclipse.gef.editparts.AbstractEditPart.addNotify(AbstractEditPart.java:260)
at org.eclipse.gef.editparts.AbstractEditPart.addChild(AbstractEditPart.java:221)
at org.eclipse.wb.gef.core.EditPart.refreshChildren(EditPart.java:120)
at org.eclipse.wb.gef.core.EditPart.refresh(EditPart.java:80)
at org.eclipse.wb.core.gef.part.AbstractComponentEditPart.refresh(AbstractComponentEditPart.java:203)
at org.eclipse.gef.editparts.AbstractEditPart.addNotify(AbstractEditPart.java:260)
at org.eclipse.gef.editparts.AbstractEditPart.addChild(AbstractEditPart.java:221)
at org.eclipse.wb.gef.core.EditPart.refreshChildren(EditPart.java:120)
at org.eclipse.wb.gef.core.EditPart.refresh(EditPart.java:80)
at org.eclipse.gef.editparts.AbstractEditPart.addNotify(AbstractEditPart.java:260)
at org.eclipse.gef.editparts.AbstractEditPart.addChild(AbstractEditPart.java:221)
at org.eclipse.wb.internal.gef.graphical.RootEditPart.setContents(RootEditPart.java:157)
at org.eclipse.wb.internal.gef.core.AbstractEditPartViewer.setInput(AbstractEditPartViewer.java:53)
at org.eclipse.wb.internal.core.editor.JavaDesignComposite.refresh(JavaDesignComposite.java:135)
at org.eclipse.wb.internal.core.editor.DesignPage.lambda$1(DesignPage.java:587)
at org.eclipse.wb.internal.core.utils.execution.ExecutionUtils.runRethrow(ExecutionUtils.java:119)
at org.eclipse.wb.internal.core.utils.execution.ExecutionUtils$2.run(ExecutionUtils.java:193)
at org.eclipse.swt.widgets.RunnableLock.run(RunnableLock.java:40)
at org.eclipse.swt.widgets.Synchronizer.runAsyncMessages(Synchronizer.java:131)
at org.eclipse.swt.widgets.Display.runAsyncMessages(Display.java:4377)
at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:4000)
at org.eclipse.jface.operation.ModalContext$ModalContextThread.block(ModalContext.java:164)
at org.eclipse.jface.operation.ModalContext.run(ModalContext.java:360)
at org.eclipse.jface.dialogs.ProgressMonitorDialog.run(ProgressMonitorDialog.java:472)
at org.eclipse.wb.internal.core.editor.DesignPage.internal_refreshGEF_withProgress(DesignPage.java:467)
at org.eclipse.wb.internal.core.editor.DesignPage.internal_refreshGEF(DesignPage.java:424)
at org.eclipse.wb.internal.core.editor.UndoManager.refreshDesignerEditor(UndoManager.java:387)
at org.eclipse.wb.internal.core.editor.UndoManager.activate(UndoManager.java:88)
at org.eclipse.wb.internal.core.editor.DesignPage.handleActiveState_True(DesignPage.java:267)
at org.eclipse.wb.internal.core.editor.DesignPage.handleActiveState(DesignPage.java:244)
at org.eclipse.wb.internal.core.editor.multi.DefaultMultiMode.showPage(DefaultMultiMode.java:129)
at org.eclipse.wb.internal.core.editor.multi.DefaultMultiMode$1.widgetSelected(DefaultMultiMode.java:65)
at org.eclipse.swt.widgets.TypedListener.handleEvent(TypedListener.java:290)
at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:91)
at org.eclipse.swt.widgets.Display.sendEvent(Display.java:4651)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1657)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1680)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1665)
at org.eclipse.swt.widgets.Widget.notifyListeners(Widget.java:1394)
at org.eclipse.swt.custom.CTabFolder.setSelection(CTabFolder.java:3269)
at org.eclipse.swt.custom.CTabFolder.onMouse(CTabFolder.java:1908)
at org.eclipse.swt.custom.CTabFolder.lambda$0(CTabFolder.java:332)
at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:91)
at org.eclipse.swt.widgets.Display.sendEvent(Display.java:4651)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1657)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1680)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1665)
at org.eclipse.swt.widgets.Widget.notifyListeners(Widget.java:1394)
at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:4422)
at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3998)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$5.run(PartRenderingEngine.java:1160)
at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:339)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.run(PartRenderingEngine.java:1051)
at org.eclipse.e4.ui.internal.workbench.E4Workbench.createAndRunUI(E4Workbench.java:153)
at org.eclipse.ui.internal.Workbench.lambda$3(Workbench.java:684)
at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:339)
at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:583)
at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:173)
at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:192)
at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:219)
at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:149)
at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:115)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:467)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:298)
at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
at java.base/java.lang.reflect.Method.invoke(Method.java:580)
at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:615)
at org.eclipse.equinox.launcher.Main.basicRun(Main.java:563)
at org.eclipse.equinox.launcher.Main.run(Main.java:1415)

<<<<<<<<<<<<***************>>>>>>>>>>>>>>>

eclipse.buildId=4.40.0.20260430-0612
java.version=21.0.10
java.vendor=Eclipse Adoptium
BootLoader constants: OS=macosx, ARCH=aarch64, WS=cocoa, NL=en_GB
Framework arguments: -product org.eclipse.epp.package.jee.product -keyring /Users/dave/.eclipse_keyring
Command-line arguments: -os macosx -ws cocoa -arch aarch64 -product org.eclipse.epp.package.jee.product -keyring /Users/dave/.eclipse_keyring

org.eclipse.jface
Warning
Wed May 13 11:45:04 BST 2026
Keybinding conflicts occurred. They may interfere with normal accelerator operation.

I am running version 1.24.0.202605021947

The issue seems to specific to one JFrame.

I have simplified the form to try and identify the problem but I get inconsistent results.

If I remove the "System Log" tab from the screen I don't get the error. So I simplified further and removed everything except that one tab, but then it worked with it. Is there any way to narrow down what WindowBuilder is parsing when the error occurs ?

C4J · 2026-05-13T12:00:28Z

C4J
May 13, 2026
Author

I think I've found a problem with WindowBuilder itself.

	tabbedPane.addTab("SFTP", null, (Component) sftp_common_Tab_Panel, "SFTP Settings");
	tabbedPane.addTab("Put Properties", null, (Component) sftp_put_Tab_Panel, "SFTP Put Settings");
	tabbedPane.addTab("Get Properties", null, (Component) sftp_get_Tab_Panel, "SFTP Get Settings");
	tabbedPane.addTab("jsch Properties", null, (Component) propertes_Tab_Panel, "SFTP Put");
	tabbedPane.addTab("Email Properties", null, (Component) email_Tab_Panel, "Email Settings");
	tabbedPane.addTab("Put Log", null, scrollPane_Put_Log, "Put Activity Log");
	tabbedPane.addTab("Get Log", null, scrollPane_Get_Log, "Get Activity Log");
	tabbedPane.addTab("System Log",null,scrollPane_System_Log,"System Log");

If I comment out any 1 of the above lines the Frame will appear in design mode. If I try and show all of them it won't work.

0 replies

C4J · 2026-05-13T12:57:01Z

C4J
May 13, 2026
Author

Ok - I created new JFrame and added all the components back in one at a time.

Here is my code and I think I found the problem which is a surprise to me.

You will see a line tabbedPane.addTab("1234567890", null, sftp_put_Tab_Panel, null); which has a tab using a 10 character title. If I try and open this Frame with window builder I get the crash above. If I remove a character "123456789" for example I don't get the crash (exception).

package com.commander4j.gui.frame;

import java.awt.EventQueue;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.EmptyBorder;
import javax.swing.JTabbedPane;
import javax.swing.JScrollPane;
import javax.swing.ScrollPaneConstants;

public class Tabs extends JFrame {

	private static final long serialVersionUID = 1L;
	private JPanel contentPane;

	/**
	 * Launch the application.
	 */
	public static void main(String[] args) {
		EventQueue.invokeLater(new Runnable() {
			public void run() {
				try {
					Tabs frame = new Tabs();
					frame.setVisible(true);
				} catch (Exception e) {
					e.printStackTrace();
				}
			}
		});
	}

	/**
	 * Create the frame.
	 */
	public Tabs() {
		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		setBounds(100, 100, 948, 582);
		contentPane = new JPanel();
		contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
		setContentPane(contentPane);
		contentPane.setLayout(null);

		JTabbedPane tabbedPane = new JTabbedPane(JTabbedPane.TOP);
		tabbedPane.setFocusable(false);
		tabbedPane.setBounds(36, 21, 705, 504);
		contentPane.add(tabbedPane);

		JPanel sftp_common_Tab_Panel = new JPanel();
		sftp_common_Tab_Panel.setLayout(null);
		tabbedPane.addTab("SFTP", null, sftp_common_Tab_Panel, null);


		JPanel sftp_put_Tab_Panel = new JPanel();
		sftp_put_Tab_Panel.setLayout(null);
		tabbedPane.addTab("1234567890", null, sftp_put_Tab_Panel, null);


		JPanel sftp_get_Tab_Panel = new JPanel();
		sftp_get_Tab_Panel.setLayout(null);
		tabbedPane.addTab("Get", null, sftp_get_Tab_Panel, null);


		JPanel propertes_Tab_Panel = new JPanel();
		propertes_Tab_Panel.setLayout(null);
		tabbedPane.addTab("Tab 4", null, propertes_Tab_Panel, null);


		JPanel email_Tab_Panel = new JPanel();
		email_Tab_Panel.setLayout(null);
		tabbedPane.addTab("Tab 5", null, email_Tab_Panel, null);

		JPanel panel_6 = new JPanel();
		panel_6.setLayout(null);
		tabbedPane.addTab("Tab 6", null, panel_6, null);

		JPanel panel_7 = new JPanel();
		panel_7.setLayout(null);
		tabbedPane.addTab("Tab 7", null, panel_7, null);

		JPanel panel_8 = new JPanel();
		panel_8.setLayout(null);
		tabbedPane.addTab("Tab 8", null, panel_8, null);

		JPanel panel_9 = new JPanel();
		panel_9.setLayout(null);
		tabbedPane.addTab("Tab 9", null, panel_9, null);

		JScrollPane scrollPane_1 = new JScrollPane();
		scrollPane_1.setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER);
		tabbedPane.addTab("New tab", null, scrollPane_1, null);

		JScrollPane scrollPane_2 = new JScrollPane();
		scrollPane_2.setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER);
		tabbedPane.addTab("New tab", null, scrollPane_2, null);

	}
}

0 replies

C4J · 2026-05-13T13:16:41Z

C4J
May 13, 2026
Author

What I have done above does replicate the issue I am seeing, but that actual number of characters may be a trigger for something else. I changed the number of characters to 9 and then added a single character to the next tab and the problem was also apparent. Most peculiar.

0 replies

C4J · 2026-05-13T13:29:30Z

C4J
May 13, 2026
Author

I have replicated this with WindowBuilder 1.23 and 1.24

0 replies

C4J · 2026-05-13T16:27:13Z

C4J
May 13, 2026
Author

I have tried with Eclipse 2026-03 and 2026-06. Step by step screendumps attached.

0 replies

C4J · 2026-05-13T16:51:17Z

C4J
May 13, 2026
Author

This maybe rubbish - but Claude AI has had a look at my test program and a download of windowbuilder source from github and has come up with this theory :-

Bug is in WindowBuilder. The exact line:

// org.eclipse.wb.swing/.../JTabbedPaneInfo.java:113
Rectangle bounds = CoordinateUtils.get(pane.getBoundsAt(i));

is passing the result of JTabbedPane.getBoundsAt(i) straight into CoordinateUtils.get(java.awt.Rectangle) (line 49 of CoordinateUtils.java), which dereferences o.x with no null check.

And JTabbedPane.getBoundsAt(int) is documented to return null — straight from the JDK 21 source:

▎ Returns the tab bounds at index. If the tab at this index is not currently visible in the UI, then returns null. If there is no UI set on this tabbedpane, then returns null.

So when one tab is wide enough that the UI delegate decides it isn't currently visible (e.g. it doesn't fit and gets clipped/scrolled out), getBoundsAt legitimately returns null and WindowBuilder NPEs.

Why long text triggers it specifically on macOS: WindowBuilder renders your Swing live in-process. On macOS the default L&F is Aqua, whose AquaTabbedPaneCopyFromBasicUI enables a scrollable / overflow
tab layout — tabs that don't fit in the visible header strip are treated as not-currently-visible and getTabBounds returns null for them. BasicTabbedPaneUI (Metal etc.) uses WRAP and always produces a
Rectangle, which is why the cross-platform L&F doesn't reproduce it.

Fix in WindowBuilder

Line 113 needs a null guard. Minimal patch in JTabbedPaneInfo.getTabs():

java.awt.Rectangle rawBounds = pane.getBoundsAt(i);
if (rawBounds == null) {
continue; // tab not currently visible — skip, don't NPE
}
Rectangle bounds = CoordinateUtils.get(rawBounds);
tabs.add(new JTabbedPaneTabInfo(this, component, bounds));

Worth reporting upstream — the Javadoc on getBoundsAt has documented the null return for years.

Workarounds (without patching WB)

Shorten the offending tab title so all tabs fit Aqua's header strip.
Force Metal at the top of Tabs.main (or in a static {} block) so WB renders with Metal instead of Aqua:
try { UIManager.setLookAndFeel(UIManager.getCrossPlatformLookAndFeelClassName()); }
catch (Exception ignored) {}
WindowBuilder evaluates static initializers and the constructor when rendering, so this swaps the UI delegate to BasicTabbedPaneUI and the NPE goes away.

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