A design pattern is a general repeatable solution to a commonly occurring problem in software design.

Design Patterns,

• Can speed up the development process by providing tested, proven development paradigms.
• Improve code readability for coders and architects familiar with the patterns.
• Provide general solutions, documented in a format that doesn't require specifics tied to a particular problem.
• Allow developers to communicate using well-known, well understood names for software interactions.
• Reusing design patterns helps to prevent subtle issues that can cause major problems.

These design patterns are all about class instantiation.

• 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

These design patterns are all about Class and Object composition.

• 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

These design patterns are all about Class's objects communication.

• 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