catch CannotUndoException : CannotUndoException « javax.swing.undo « Java by API

1. Java by API
2. javax.swing.undo
3. CannotUndoException

catch CannotUndoException

import java.awt.BorderLayout;
import java.awt.Component;
import java.awt.Container;
import java.awt.event.ActionEvent;

import javax.swing.AbstractAction;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.JToolBar;
import javax.swing.UIManager;
import javax.swing.undo.CannotUndoException;
import javax.swing.undo.UndoManager;

public class MainClass {

  public static void main(final String args[]) {
    JFrame frame = new JFrame("Undo Sample");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    JTextArea textArea = new JTextArea();
    JScrollPane scrollPane = new JScrollPane(textArea);

    UndoManager manager = new UndoManager();
    textArea.getDocument().addUndoableEditListener(manager);

    JToolBar toolbar = new JToolBar();
    JButton undoButton = new JButton(new UndoAction(manager, (String) UIManager
        .get("AbstractUndoableEdit.undoText")));
    toolbar.add(undoButton);

    Container content = frame.getContentPane();
    content.add(toolbar, BorderLayout.NORTH);
    content.add(scrollPane, BorderLayout.CENTER);
    frame.setSize(300, 150);
    frame.setVisible(true);

  }
}

abstract class UndoRedoAction extends AbstractAction {
  UndoManager undoManager = new UndoManager();

  String errorMessage = "Cannot undo";

  String errorTitle = "Undo Problem";

  protected UndoRedoAction(UndoManager manager, String name) {
    super(name);
    undoManager = manager;
  }

  public void setErrorMessage(String newValue) {
    errorMessage = newValue;
  }

  public void setErrorTitle(String newValue) {
    errorTitle = newValue;
  }

  protected void showMessage(Object source) {
    if (source instanceof Component) {
      JOptionPane.showMessageDialog((Component) source, errorMessage, errorTitle,
          JOptionPane.WARNING_MESSAGE);
    } else {
      System.err.println(errorMessage);
    }
  }
}

class UndoAction extends UndoRedoAction {
  public UndoAction(UndoManager manager, String name) {
    super(manager, name);
    setErrorMessage("Cannot undo");
    setErrorTitle("Undo Problem");
  }

  public void actionPerformed(ActionEvent actionEvent) {
    try {
      undoManager.undo();
    } catch (CannotUndoException cannotUndoException) {
      showMessage(actionEvent.getSource());
    }
  }
}
           
       

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