Remember, knowing concepts like abstraction, inheritance, and polymorphism do not make you a good object oriented designer. A design guru thinks about how to create flexible designs that are maintainable and that can cope with change.
Provides an interface for creating objects in a superclass, but allows subclasses to alter the type of objects that will be created.
Lets you produce families of related objects without specifying their concrete classes.
Lets you ensure that a class has only one instance, while providing a global access point to this instance.
Provides a unified interface that allows objects with incompatible interfaces to collaborate.
Lets you compose objects into tree structures and then work with these structures as if they were individual objects.
Lets you attach new behaviors to objects by placing these objects inside special wrapper objects that contain the behaviors.
Provides a simplified interface to a library, a framework, or any other complex set of classes.
Lets you provide a substitute or placeholder for another object. A proxy controls access to the original object, allowing you to perform something either before or after the request gets through to the original object.
Turns a request into a stand-alone object that contains all information about the request. This transformation lets you parameterize methods with different requests, delay or queue a request's execution, and support undoable operations.
Lets you traverse elements of a collection without exposing its underlying representation (list, stack, tree, etc.).
Lets you define a subscription mechanism to notify multiple objects about any events that happen to the object they're observing.
Lets an object alter its behavior when its internal state changes. It appears as if the object changed its class.
Lets you define a family of algorithms, put each of them into a separate class, and make their objects interchangeable.
Defines the skeleton of an algorithm in the superclass but lets subclasses override specific steps of the algorithm without changing its structure.
- Eric Freeman, Elisabeth Freeman "Head First Design Patterns" 📘
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