import org.openide.actions.UndoAction; //导入依赖的package包/类
private void undo() throws Exception {
    final UndoAction ua = SystemAction.get(UndoAction.class);
    assertNotNull("Cannot obtain UndoAction", ua);
    while (ua.isEnabled()) {
        SwingUtilities.invokeAndWait(new Runnable() {

            public void run() {
                ua.performAction();
            }
        });
    }
}
 

import org.openide.actions.UndoAction; //导入依赖的package包/类
protected @Override void updateActions() {
    addSystemActionMapping(cutAction, javax.swing.text.DefaultEditorKit.cutAction);
    addSystemActionMapping(copyAction, javax.swing.text.DefaultEditorKit.copyAction);
    addSystemActionMapping(pasteAction, org.openide.actions.PasteAction.class);
    // #69077 - DeleteAction now delegates to deleteNextCharAction
    addSystemActionMapping(deleteNextCharAction, "delete");
    addSystemActionMapping(showPopupMenuAction, org.openide.actions.PopupAction.class);

    addSystemActionMapping(gotoAction, org.openide.actions.GotoAction.class);

    addSystemActionMapping(undoAction, org.openide.actions.UndoAction.class);
    addSystemActionMapping(redoAction, org.openide.actions.RedoAction.class);
}
 

import org.openide.actions.UndoAction; //导入依赖的package包/类
public @Override void actionPerformed(ActionEvent evt, JTextComponent target) {
    Document doc = target.getDocument();
    if (doc.getProperty(BaseDocument.UNDO_MANAGER_PROP) != null ||
        doc.getProperty(UndoManager.class) != null )
    { // Basic way of undo
        super.actionPerformed(evt, target);
    } else { // Deleagte to system undo action
        // Delegate to system undo action
        UndoAction ua = (UndoAction)SystemAction.get(UndoAction.class);
        if (ua != null && ua.isEnabled()) {
            ua.actionPerformed(evt);
        }
    }
}
 

import org.openide.actions.UndoAction; //导入依赖的package包/类
private void registerEditorActions() {
    registerAction(SystemAction.get(UndoAction.class), "control Z");
    registerAction(SystemAction.get(RedoAction.class), "control R");
    registerAction(SystemAction.get(org.openide.actions.SaveAction.class), "control S");
    registerAction(new TogleCommentAction(editor), "control /");
}