A design pattern is a general repeatable solution to a commonly occurring problem in software design. It is a description or template for how to solve a problem that can be used in many different situations.
Creational design patterns
These design patterns are all about class instantiation. This pattern can be further divided into class-creation patterns and object-creational patterns. While class-creation patterns use inheritance effectively in the instantiation process, object-creation patterns use delegation effectively to get the job done.
- Abstract Factory: Creates an instance of several families of classes
- Builder: Separates object construction from its representation
- Factory Method: Creates an instance of several derived classes
- Object Pool: Avoid expensive acquisition and release of resources by recycling objects that are no longer in use
- Prototype: A fully initialized instance to be copied or cloned
- Singleton: A class of which only a single instance can exist
Structural design patterns
These design patterns are all about Class and Object composition. Structural class-creation patterns use inheritance to compose interfaces. Structural object-patterns define ways to compose objects to obtain new functionality.
- Adapter: Match interfaces of different classes
- Bridge: Separates an object’s interface from its implementation
- Composite: A tree structure of simple and composite objects
- Decorator: Add responsibilities to objects dynamically
- Facade: A single class that represents an entire subsystem
- Flyweight: A fine-grained instance used for efficient sharing
- Private Class Data: Restricts accessor/mutator access
- Proxy: An object representing another object
Behavioral design patterns
These design patterns are all about Class’s objects communication. Behavioral patterns are those patterns that are most specifically concerned with communication between objects.
- Chain of responsibility: A way of passing a request between a chain of objects
- Command: Encapsulate a command request as an object
- Interpreter: A way to include language elements in a program
- Iterator: Sequentially access the elements of a collection
- Mediator: Defines simplified communication between classes
- Memento: Capture and restore an object’s internal state
- Null Object: Designed to act as a default value of an object
- Observer: A way of notifying change to a number of classes
- State: Alter an object’s behavior when its state changes
- Strategy: Encapsulates an algorithm inside a class
- Template method: Defer the exact steps of an algorithm to a subclass
- Visitor: Defines a new operation to a class without change