Apr 4th, 2023
The Memento Pattern is a behavioral design pattern that allows an object to save and restore its internal state without violating encapsulation. This pattern is useful when we need to capture the state of an object at a particular point in time and be able to restore it later.
In the Memento Pattern, we have three main components:
- Originator: This is the object whose state we want to capture and restore. It creates a memento object that contains a snapshot of its current state and also restores its state from a memento object.
- Memento: This is an object that contains a snapshot of the state of the originator object. It should only be accessible to the originator object and should not be modified by any other objects.
- Caretaker: This is an object that is responsible for storing and retrieving mementos. It can only store and retrieve mementos, it cannot modify or access their contents.
To use the Memento Pattern, we first create an Originator object whose state we want to capture and restore. The Originator object creates a Memento object that contains a snapshot of its current state. The Memento object is then passed to the Caretaker object, which stores it.
Later, if we want to restore the state of the Originator object, we pass the Memento object back to the Originator object, which restores its state from the Memento object.
Let's take an example of a text editor that allows users to undo and redo their actions. In this case, we can use the Memento Pattern to save the state of the document before each action and restore it if the user wants to undo the action.
First, we define the Originator object as the document that the user is editing. We create a Memento object that contains a snapshot of the current state of the document. We then define the Caretaker object as the object that stores the Memento objects.
When the user performs an action, we create a new Memento object that contains a snapshot of the current state of the document and pass it to the Caretaker object, which stores it. If the user wants to undo an action, we retrieve the most recent Memento object from the Caretaker object and pass it back to the Originator object, which restores the state of the document to the state in the Memento object.
By using the Memento Pattern, we can create a flexible and extensible system that allows users to undo and redo their actions without violating encapsulation.
In conclusion, the Memento Pattern is a powerful behavioral design pattern that allows us to capture and restore the state of an object without violating encapsulation. By using the pattern, we can create flexible and extensible systems that are easier to maintain and modify.