The Observer pattern is a behavioral pattern that defines a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically. The main idea behind the Observer pattern is to provide a way for objects to be notified of changes in the state of another object without tightly coupling them together. This allows for a more flexible and maintainable design by separating the concerns of the objects....

The Memento pattern is a behavioral pattern that allows you to capture and externalize an object’s internal state so that the object can be restored to that state later without violating encapsulation. The main idea behind the Memento pattern is to provide a way to save and restore an object’s state without exposing its internal structure. This allows you to save the state of an object at a particular point in time and restore it later if necessary....

The Mediator pattern is a behavioral pattern that defines an object that encapsulates how a set of objects interact with each other. It promotes loose coupling by keeping objects from referring to each other explicitly and allows for their interaction to be centralised in a mediator object. The main idea behind the Mediator pattern is to reduce the complexity of the interactions between objects by introducing a mediator object that handles the communication between them....

The Iterator pattern is a behavioral pattern that provides a way to access the elements of an aggregate object sequentially without exposing its underlying representation. The main idea behind the Iterator pattern is to provide a uniform interface for traversing different types of collections, such as arrays, lists, trees, and so on. This interface allows clients to iterate over the elements of a collection without having to know about the internal structure of the collection....

The Command pattern is a behavioral pattern that allows you to encapsulate a request as an object, thereby allowing you to parameterize clients with different requests, queue or log requests, and support undoable operations. The main idea behind the Command pattern is to separate the object that invokes the operation from the object that knows how to perform the operation. This separation allows you to decouple the client that sends the request from the receiver that performs the request, and also allows you to implement the request as an object that can be passed as a parameter, stored, or manipulated like any other object....