java怎么撤销

<code class="java">class Editor {
    private Stack<String> history = new Stack<>();

    public void setText(String text) {
        history.push(currentText);
        currentText = text;
    }

    public void undo() {
        if (!history.isEmpty()) {
            currentText = history.pop();
        }
    }
}</code>

<code class="java">interface Command {
    void execute();
    void undo();
}

class SetTextCommand implements Command {
    private Editor editor;
    private String text;

    public SetTextCommand(Editor editor, String text) {
        this.editor = editor;
        this.text = text;
    }

    @Override
    public void execute() {
        editor.setText(text);
    }

    @Override
    public void undo() {
        editor.undo();
    }
}

class CommandQueue {
    private List<Command> commands = new ArrayList<>();

    public void addCommand(Command command) {
        commands.add(command);
    }

    public void undo() {
        if (!commands.isEmpty()) {
            Command command = commands.remove(commands.size() - 1);
            command.undo();
        }
    }
}</code>