The Iterator stores the Memento internally. State is like Strategy except in its intent. State objects are often Singleton s. Strategy lets you change the guts of an object. Decorator lets you change the skin.
Strategy is to algorithm.
Strategy has 2 different implementations, the first is similar to State . Strategy is like Template Method except in its granularity. Template Method uses inheritance to vary part of an algorithm. Strategy uses delegation to vary the entire algorithm. The Visitor pattern is like a more powerful Command pattern because the visitor may initiate whatever is appropriate for the kind of object it encounters.