#Design patterns Notes from design patterns books and trainings
- Identify the aspects of your application that vary and separate them from what stays the same
- Program to an interface, not an implementation
- Favor composition over inheritance
- Strive for loosely coupled designs between objects that interact
- Code should be closed to modification and open to extension
- Dependency inversion - dependency upon abstractions, not concrete classes
- Principle of Least Knowledge - talk only to your immediate friends
- The Hollywood principle - Don't call us, we'll call you
- Single responsibility - a class should have only one reason to change
##Strategy Defines a family of algorithms, encapsulates each one, and makes them interchangeable. Strategy lets the algorithm vary independently from clients that use it.
##Observer Defines one-to-many dependency between objects so that when one object change state, all of its dependents are notified and updated automatically.
##Decorator Attaches additional responsibilities to an object dynamically. Decorators provide a flexible alternative to subclassing for extending functionality.
##Factory method Defines an interface for creating an object, but lets subclasses decide which class to instantiate. Factory method lets a class defer instantiation to subclasses.
##Abstract factory Provides an interface for creating families of related or dependent objects without specifying their concrete classes.
##Singleton Ensures a class has only one instance, and provides a global point of access to it.
##Command Encapsulates a request as an object, thereby letting you parametrize other objects with different requests, queue or log requests, and support undoable operations.
##Adapter Converts the interface of a class into another interface the clients expect. Adapter lets classes work together that couldn't otherwise because of incompatible interfaces.
##Facade Provides a unified interface to a set of interfaces in a subsystem. Facade defines a higher level interface that makes the subsystem easier to use.
##The template method Defines the skeleton of an algorithm in a method, deferring some steps to subclasses. Template method lets subclasses redefine certain steps of an algorithm without changing the algorithm's structure.
##Iterator Provides a way to access the elements of an aggregate object sequentially without exposing its underlying representation.
##Composite Allows you to compose objects into tree structures to represent part-whole hierarchies. Composite lets clients treat individual objects and compositions of objects uniformly.
##The state pattern Allows an object to alter its behavior when its internal state change. The object will appear to change its class.
##Proxy Provides a surrogate or placeholder for another object to control access to it.