Memento Pattern

1. Definition

Save an object’s state so it can be restored later. Undo logic such as Ctrl+Z can use this pattern.

2. UML

3. Java

3.1. Object Being Saved

public class Article
{
    private String title;
    private String content;

    public Article(String title, String content)
    {
        this.title = title;
        this.content = content;
    }

    public String getTitle()
    {
        return title;
    }

    public void setTitle(String title)
    {
        this.title = title;
    }

    public String getContent()
    {
        return content;
    }

    public void setContent(String content)
    {
        this.content = content;
    }

    public ArticleMemento saveToMemento()
    {
        return new ArticleMemento(this.title, this.content);
    }

    public void undoFromMemento(ArticleMemento memento)
    {
        this.title = memento.getTitle();
        this.content = memento.getContent();
    }

    @Override
    public String toString()
    {
        return "Article{" + "title='" + title + '\'' + ", content='" + content + '\'' + '}';
    }
}

3.2. Memento

• ArticleMemento

public class ArticleMemento
{
    private String title;
    private String content;

    public ArticleMemento(String title, String content)
    {
        this.title = title;
        this.content = content;
    }

    public String getTitle()
    {
        return title;
    }

    public String getContent()
    {
        return content;
    }
}

• ArticleMementoManager

public class ArticleMemento
{
    private String title;
    private String content;

    public ArticleMemento(String title, String content)
    {
        this.title = title;
        this.content = content;
    }

    public String getTitle()
    {
        return title;
    }

    public String getContent()
    {
        return content;
    }
}

3.3. Client

public class Client
{
    public static void main(String[] args)
    {
        Article article = new Article("Title 1", "Content 1");
        System.out.println("Initially: " + article);

        ArticleMemento articleMemento = article.saveToMemento();

        ArticleMementoManager mementoManager = new ArticleMementoManager();
        mementoManager.addMemento(articleMemento);


        article.setContent("Content 2");
        article.setTitle("Title 2");
        System.out.println("After modification: " + article);


        ArticleMemento memento = mementoManager.getMemento();
        article.undoFromMemento(memento);
        System.out.println("Restored from memento: " + article);

    }
}