Using undo and redo for JTextArea

Question

I am making a text editor using Java swing. I am using JTextArea for the same. I want to know how I can use Undo and Redo functionality in JTextArea as I am not able to use

Answer 1

I created a simple class that can assign undo functionality to a JTextcomponent (JTextField, JTextArea, etc.) with a single method call:

UndoTool.addUndoFunctionality(area);

or alternatively construct a new JTextArea with the undo functionality pre-assigned:

UndoTool.createJTextFieldWithUndo();

Here is the implementation of the utility class:

public class UndoTool {
    private static final String REDO_KEY = "redo";
    private static final String UNDO_KEY = "undo";

    private JTextComponent component;
    private KeyStroke undo = KeyStroke.getKeyStroke("control Z");
    private KeyStroke redo = KeyStroke.getKeyStroke("control Y");

    public UndoTool(JTextComponent component) {
        this.component = component;
    }

    public void setUndo(KeyStroke undo) {
        this.undo = undo;
    }

    public void setRedo(KeyStroke redo) {
        this.redo = redo;
    }

    public static void addUndoFunctionality(JTextComponent component) {
        UndoTool tool = new UndoTool(component);
        UndoManager undo = tool.createAndBindUndoManager();
        tool.bindUndo(undo);
        tool.bindRedo(undo);
    }

    public static JTextArea createJTextAreaWithUndo() {
        JTextArea area = new JTextArea();
        addUndoFunctionality(area);
        return area;
    }

    public static JTextField createJTextFieldWithUndo() {
        JTextField field = new JTextField();
        addUndoFunctionality(field);
        return field;
    }

    public UndoManager createAndBindUndoManager() {
        Check.notNull(component);

        UndoManager manager = new UndoManager();
        Document document = component.getDocument();
        document.addUndoableEditListener(event -> manager.addEdit(event.getEdit()));
        return manager;
    }

    public void bindRedo(UndoManager manager) {
        component.getActionMap().put(REDO_KEY, new AbstractAction(REDO_KEY) {
            @Override
            public void actionPerformed(ActionEvent evt) {
                try {
                    if (manager.canRedo()) {
                        manager.redo();
                    }
                } catch (CannotRedoException ignore) {
                }
            }
        });
        component.getInputMap().put(redo, REDO_KEY);
    }

    public void bindUndo(UndoManager manager) {
        component.getActionMap().put(UNDO_KEY, new AbstractAction(UNDO_KEY) {
            @Override
            public void actionPerformed(ActionEvent evt) {
                try {
                    if (manager.canUndo()) {
                        manager.undo();
                    }
                } catch (CannotUndoException ignore) {
                }
            }
        });
        component.getInputMap().put(undo, UNDO_KEY);
    }
}