OO设计模式小结 -

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OO设计模式小结

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DesignPattern

OO 设计模式编程 prototype Access

引用自<head first design pattern>以及wiki

OO : Abstraction; Encapsulation; Polymorphism; Inheritance

OO principle:
    * Encapsulate what varies.(basic rule, Strategy Pattern)封装变化；
    * Favor composition over inheritance.多用组合，少用继承；
    * Program to interfaces, not implementations.针对接口编程，不针对实现编程；
    * Strive for loosely coupled designs between objects that interact.为交互对象之间的松耦合设计而努力；
    * Classes should be open for extension but closed for modification.类应该对扩展开放，对修改关闭；
    * Depend on abstractions. Do not depend on concrete classes.（The Dependency Inversion Principle）依赖抽象，不要依赖具体类；
    * Only talk to your friends.（Principle of Least Knowledge）只和朋友交谈；
    * Don't call us, we'll call you.（The Hollywood Principle，High-level components control when and how low-level components can participate in the computation. But never call high-level components directly.）别找我，我会找你；
    * A class should have only one reason to change.（Single Responsibility Principle）类应该只有一个改变的理由；

Creational patterns:
Abstract factory : Provide an interface for creating families of related or dependent objects without specifying their concrete classes.
Factory method : 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 : Separate the construction of a complex object from its representation so that the same construction process can create different representations.
Prototype: Specify the kinds of objects to create using a prototypical instance, and create new objects by copying this prototype.
Singleton : Ensure a class has only one instance, and provide a global point of access to it.

Structural patterns:
Adapter : 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 : Decouple an abstraction from its implementation so that the two can vary independently.
Composite : Compose objects into tree structures to represent part-whole hierarchies. Composite lets clients treat individual objects and compositions of objects uniformly.
Decorator: Attach additional responsibilities to an object dynamically keeping the same interface. Decorators provide a flexible alternative to subclassing for extending functionality.
Facade : Provide a unified interface to a set of interfaces in a subsystem. Facade defines a higher-level interface that makes the subsystem easier to use.
Flyweight: Use sharing to support large numbers of fine-grained objects efficiently.
Proxy : Provide a surrogate or placeholder for another object to control access to it.

Behavioral patterns
Chain of responsibility : 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 : Encapsulate a request as an object, thereby letting you parameterize clients with different requests, queue or log requests, and support undoable operations.
Interpreter: Given a language, define a representation for its grammar along with an interpreter that uses the representation to interpret sentences in the language.
Iterator : Provide a way to access the elements of an aggregate object sequentially without exposing its underlying representation.
Mediator : 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 : Without violating encapsulation, capture and externalize an object's internal state so that the object can be restored to this state later.
Observer : Define a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically.
State : Allow an object to alter its behavior when its internal state changes. The object will appear to change its class.
Strategy : Define a family of algorithms, encapsulate each one, and make them interchangeable. Strategy lets the algorithm vary independently from clients that use it.
Template method : 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 : 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.

/** 
  * State 
  */
public class GumballMachine {
    State souldOutStates;
    State noQuarterStates;
    State hasQuarterStates;
    State souldStates;
    State winnerStates;

    State state=souldOutState;
    int count=0;
  
    ...
}

/** Flyweight Pattern
  * 用途：当一个类有许多的实例，而这些实例能被统一方法控制的时候。提高效率
  * 优点：减少运行时对象实例的个数，节省内存；将许多“虚拟”对象的状态集中管理；
  * 缺点：单个的逻辑实例将无法拥有独立而不同的行为
  * /
//in pattern
public class TreeManager{
    ArrayList treeArray;

    displayTrees(){
    //设置所有树的数组位置
         display(x,y,age);
    }
}

class Tree{       //一个单独的没有状态的树对象
    display(x,y,age){}
}

//withoutPattern
public class Tree{
    int xCoord;
    int yCoord;
    int age;
    
    display(){}
}

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