Thursday, 20 January 2005 21:45

Without violating encapsulation, capture and externalize an object's internal state so that the object can be restored to this state later.

Source code

/**
 * Creates a memento containing a snapshot of its current internal state.
 * Uses the memento to restore its internal state.
 * @role __Originator
 */
public class Originator {
        public Memento createMemento() {
                return new ConcreteMemento(this);        }

        public void setMemento(Memento memento) {
                if (memento instanceof ConcreteMemento) {
                        // extract state from memento
                }
        }

}

/**
 * Represents narrow interface of the memento visible to Caretaker
 * @role __Memento
 */
public interface Memento {
}

/**
 * Stores internal state of the Originator object. 
 * This is sort of wide memento interface,
 * visible to Originator.
 */
public class ConcreteMemento implements Memento {
        public ConcreteMemento(Originator originator) {
                // initialize memento with originator's state
        }

}

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