import java.awt.BorderLayout; import java.awt.GridLayout; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import javax.swing.JButton; import javax.swing.JFrame; import javax.swing.JPanel; import javax.swing.JScrollPane; import javax.swing.JTextArea; import javax.swing.event.UndoableEditEvent; import javax.swing.event.UndoableEditListener; import javax.swing.undo.CannotRedoException; import javax.swing.undo.UndoManager; public class UndoRedoTextArea extends JFrame {  protected JTextArea textArea = new JTextArea();  protected UndoManager undoManager = new UndoManager();  protected JButton undoButton = new JButton("Undo");  protected JButton redoButton = new JButton("Redo");  public UndoRedoTextArea() {    super("Undo/Redo Demo");    undoButton.setEnabled(false);    redoButton.setEnabled(false);    JPanel buttonPanel = new JPanel(new GridLayout());    buttonPanel.add(undoButton);    buttonPanel.add(redoButton);    JScrollPane scroller = new JScrollPane(textArea);    getContentPane().add(buttonPanel, BorderLayout.NORTH);    getContentPane().add(scroller, BorderLayout.CENTER);    textArea.getDocument().addUndoableEditListener(        new UndoableEditListener() {          public void undoableEditHappened(UndoableEditEvent e) {            undoManager.addEdit(e.getEdit());            updateButtons();          }        });    undoButton.addActionListener(new ActionListener() {      public void actionPerformed(ActionEvent e) {        try {          undoManager.undo();        } catch (CannotRedoException cre) {          cre.printStackTrace();        }        updateButtons();      }    });    redoButton.addActionListener(new ActionListener() {      public void actionPerformed(ActionEvent e) {        try {          undoManager.redo();        } catch (CannotRedoException cre) {          cre.printStackTrace();        }        updateButtons();      }    });    setSize(400, 300);    setVisible(true);  }  public void updateButtons() {    undoButton.setText(undoManager.getUndoPresentationName());    redoButton.setText(undoManager.getRedoPresentationName());    undoButton.setEnabled(undoManager.canUndo());    redoButton.setEnabled(undoManager.canRedo());  }  public static void main(String argv[]) {    new UndoRedoTextArea();  } }  

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