These patterns cover algorithms and the assignment of responsibilities between objects.
Iterator – this pattern is concerned with allowing iterative access to a composition without exposing the underlying implementation.
Mediator – the mediator pattern is concerned with ensuring loose coupling between objects by defining interfaces that allow them to interact without knowledge of each others’ internals.
Observer – this pattern defines a one-many dependency in which one object – called the subject – notifies subscribing objects of changes in its state.
State – this pattern is about allowing an object to change its behaviour when its state changes. The object will appear to change its class.
The Gang of Four give the example of a TCP connection – which will respond differently to datagrams depending if it is in the LISTEN, ESTABLISHED or CLOSED state. In each of these cases a different subclass will handle behaviour, though a common interface is used by all three.
Strategy – this pattern allows objects with different algorithms to operate through a common interface. Typical examples in text books and lecture notes are including paper aeroplanes and rubber ducks in collections of aircraft and avians!
So, for instance, all aircraft may have a
fly() method in their abstract interface, but the concrete implementation for the paper aeroplane implements behaviour appropriate for that type of craft.
Template Method - this pattern creates a skeleton for an algorithm but allows subclasses to over-ride specific parts.
Visitor – the visitor software pattern is concerned with allowing new algorithms to be applied to an object without changing the object itself. Instead a new visitor class implements the visitor interface. In this way many new methods can be dynamically added to a class.
- The “Gang of Four” software patterns (cartesianproduct.wordpress.com)
- Creational patterns (cartesianproduct.wordpress.com)
- GRASP software patterns (cartesianproduct.wordpress.com)
- Design Patterns in the JDK (javacodegeeks.com)
- OO Design Patterns (ashokabhat.wordpress.com)
- Dissolving patterns (robey.lag.net)
- Let’s clear the confusion regarding multiple implementation inheritance in C++ (gastonnusimovich.wordpress.com)
- Patterns (siddheshabhivyakty.wordpress.com)
- Model View Controller: History, theory and usage (amix.dk)