暑期实习的时候做了一次presentation on design pattern，以下是做的draft(由于公司算半个外企，用的英文;)
Design patterns are recurring solutions to software design problems you find again and again in real-world application development.
Patterns are about design and interaction of objects, as well as providing a communication platform concerning elegant,
reusable solutions to commonly encountered programming challenges.
They are categorized in three groups: Creational, Structural, and Behavioral.
Abstract Factory
definition
Provide an interface for creating families of related or dependent objects without specifying their concrete classes.
Factory Method
definition
Define an interface for creating an object, but let subclasses decide which class to instantiate. Factory Method lets a class defer instantiation to subclasses.
Builder
definition
Separate the construction of a complex object from its representation so that the same construction process can create different representations.
Prototype
definition
Specify the kind of objects to create using a prototypical instance, and create new objects by copying this prototype.
Singleton
definition
Ensure a class has only one instance and provide a global point of access to it.
Adapter
definition
Convert the interface of a class into another interface clients expect. Adapter lets classes work together that couldn't otherwise because of incompatible interfaces.
Bridge
definition
Decouple an abstraction from its implementation so that the two can vary independently.
Composite
definition
Compose objects into tree structures to represent part-whole hierarchies. Composite lets clients treat individual objects and compositions of objects uniformly.
Decorator
definition
Attach additional responsibilities to an object dynamically. Decorators provide a flexible alternative to subclassing for extending functionality.
Facade
definition
Provide a unified interface to a set of interfaces in a subsystem. Fa鏰de defines a higher-level interface that makes the subsystem easier to use.
Flyweight
definition
Use sharing to support large numbers of fine-grained objects efficiently.
Proxy
definition
Provide a surrogate or placeholder for another object to control access to it.
Chain of Responsibility
definition
Avoid coupling the sender of a request to its receiver by giving more than one object a chance to handle the request. Chain the receiving objects and pass the request along the chain until an object handles it.
Command
definition
Encapsulate a request as an object, thereby letting you parameterize clients with different requests, queue or log requests, and support undoable operations.
Interpreter
definition
Given a language, define a representation for its grammar along with an interpreter that uses the representation to interpret sentences in the language.
Iterator
definition
Provide a way to access the elements of an aggregate object sequentially without exposing its underlying representation.
Mediator
definition
Define an object that encapsulates how a set of objects interact. Mediator promotes loose coupling by keeping objects from referring to each other explicitly, and it lets you vary their interaction independently.
Memento
definition
Without violating encapsulation, capture and externalize an object's internal state so that the object can be restored to this state later.
Observer
definition
Define a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically.
State
definition
Allow an object to alter its behavior when its internal state changes. The object will appear to change its class.
Strategy
definition
Define a family of algorithms, encapsulate each one, and make them interchangeable. Strategy lets the algorithm vary independently from clients that use it.
Template
definition
Define the skeleton of an algorithm in an operation, deferring some steps to subclasses. Template Method lets subclasses redefine certain steps of an algorithm without changing the algorithm's structure.
Visitor
definition
Represent an operation to be performed on the elements of an object structure. Visitor lets you define a new operation without changing the classes of the elements on which it operates.