Cannot create text hover for my editor in Eclipse plugin development

Question

In Eclipse plugin development, I customerize an editor which extends the CompilationUnitEditor , a customized source viewer named CLRJavaSourceViewer , which implements IJavaEditorTextHover . In the plugin.xml, I create an extension on org.eclipse.jdt.ui.javaEditorTextHover as

plugin.xml Errors in creating a text hover for my own editor.

java.lang.ClassCastException: loongplugin.editor.viewer.CLRJavaSourceViewer cannot be cast to org.eclipse.jdt.internal.ui.javaeditor.CompilationUnitEditor$AdaptedSourceViewer
    at org.eclipse.jdt.internal.ui.javaeditor.CompilationUnitEditor.handlePreferenceStoreChanged(CompilationUnitEditor.java:1573)
    at org.eclipse.ui.texteditor.AbstractTextEditor$PropertyChangeListener.propertyChange(AbstractTextEditor.java:715)
    at org.eclipse.ui.texteditor.ChainedPreferenceStore.firePropertyChangeEvent(ChainedPreferenceStore.java:164)
    at org.eclipse.ui.texteditor.ChainedPreferenceStore.handlePropertyChangeEvent(ChainedPreferenceStore.java:431)
    at org.eclipse.ui.texteditor.ChainedPreferenceStore.access$0(ChainedPreferenceStore.java:408)
    at org.eclipse.ui.texteditor.ChainedPreferenceStore$PropertyChangeListener.propertyChange(ChainedPreferenceStore.java:69)
    at org.eclipse.ui.preferences.ScopedPreferenceStore$3.run(ScopedPreferenceStore.java:382)
    at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
    at org.eclipse.ui.preferences.ScopedPreferenceStore.firePropertyChangeEvent(ScopedPreferenceStore.java:378)
    at org.eclipse.ui.preferences.ScopedPreferenceStore$2.preferenceChange(ScopedPreferenceStore.java:197)
    at org.eclipse.core.internal.preferences.EclipsePreferences$3.run(EclipsePreferences.java:896)
    at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
    at org.eclipse.core.internal.preferences.EclipsePreferences.firePreferenceEvent(EclipsePreferences.java:899)
    at org.eclipse.core.internal.preferences.EclipsePreferences.put(EclipsePreferences.java:912)
    at org.eclipse.ui.preferences.ScopedPreferenceStore.setValue(ScopedPreferenceStore.java:824)
    at org.eclipse.jdt.internal.ui.preferences.OverlayPreferenceStore.propagateProperty(OverlayPreferenceStore.java:139)
    at org.eclipse.jdt.internal.ui.preferences.OverlayPreferenceStore.propagate(OverlayPreferenceStore.java:146)
    at org.eclipse.jdt.internal.ui.preferences.AbstractConfigurationBlockPreferencePage.performOk(AbstractConfigurationBlockPreferencePage.java:98)
    at org.eclipse.jface.preference.PreferenceDialog$12.run(PreferenceDialog.java:992)
    at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
    at org.eclipse.ui.internal.JFaceUtil$1.run(JFaceUtil.java:50)
    at org.eclipse.jface.util.SafeRunnable.run(SafeRunnable.java:178)
    at org.eclipse.jface.preference.PreferenceDialog.okPressed(PreferenceDialog.java:971)
    at org.eclipse.ui.internal.dialogs.FilteredPreferenceDialog.okPressed(FilteredPreferenceDialog.java:460)
    at org.eclipse.ui.internal.dialogs.WorkbenchPreferenceDialog.okPressed(WorkbenchPreferenceDialog.java:174)
    at org.eclipse.jface.preference.PreferenceDialog.buttonPressed(PreferenceDialog.java:236)
    at org.eclipse.jface.dialogs.Dialog$2.widgetSelected(Dialog.java:619)
    at org.eclipse.swt.widgets.TypedListener.handleEvent(TypedListener.java:248)
    at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
    at org.eclipse.swt.widgets.Display.sendEvent(Display.java:4188)
    at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1467)
    at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1490)
    at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1475)
    at org.eclipse.swt.widgets.Widget.notifyListeners(Widget.java:1279)
    at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:4031)
    at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3658)
    at org.eclipse.jface.window.Window.runEventLoop(Window.java:832)
    at org.eclipse.jface.window.Window.open(Window.java:808)
    at org.eclipse.ui.internal.dialogs.WorkbenchPreferenceDialog.open(WorkbenchPreferenceDialog.java:221)
    at org.eclipse.ui.texteditor.AbstractDecoratedTextEditor$9.run(AbstractDecoratedTextEditor.java:1259)
    at org.eclipse.jface.action.Action.runWithEvent(Action.java:519)
    at org.eclipse.jface.action.ActionContributionItem.handleWidgetSelection(ActionContributionItem.java:595)
    at org.eclipse.jface.action.ActionContributionItem.access$2(ActionContributionItem.java:511)
    at org.eclipse.jface.action.ActionContributionItem$5.handleEvent(ActionContributionItem.java:420)
    at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
    at org.eclipse.swt.widgets.Display.sendEvent(Display.java:4188)
    at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1467)
    at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1490)
    at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1475)
    at org.eclipse.swt.widgets.Widget.notifyListeners(Widget.java:1279)
    at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:4031)
    at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3658)
    at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$9.run(PartRenderingEngine.java:1151)
    at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332)
    at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.run(PartRenderingEngine.java:1032)
    at org.eclipse.e4.ui.internal.workbench.E4Workbench.createAndRunUI(E4Workbench.java:148)
    at org.eclipse.ui.internal.Workbench$5.run(Workbench.java:636)
    at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332)
    at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:579)
    at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:150)
    at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:135)
    at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:196)
    at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:134)
    at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:104)
    at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:382)
    at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:236)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:648)
    at org.eclipse.equinox.launcher.Main.basicRun(Main.java:603)
    at org.eclipse.equinox.launcher.Main.run(Main.java:1465)
    at org.eclipse.equinox.launcher.Main.main(Main.java:1438)

Answer 1

CompilationUnitEditor is in an internal package, you should not be extending it (see Eclipse API Rules of Engagement ).

The editor expects the source viewer to be CompilationUnitEditor.AdaptedSourceViewer not the source viewer you are providing. Since AdaptedSourceViewer is a package private inner class of CompilationUnitEditor you cannot fix this.

You could try overriding handlePreferenceStoreChanged to fix this but expect more problems.