X.d 笔记

设计模式有个特点，就是一看模式的命名，就大致知道是干什么的，使用场景也可能会和名称上的动作相关。

命令行模式 Command

命令模式把一个请求或者操作封装到一个对象中。命令模式把发出命令的责任和执行命令的责任分割开，委派给不同的对象。命令模式允许请求的一方和发送的一方独立开来，使得请求的一方不必知道接收请求的一方的接口，更不必知道请求是怎么被接收，以及操作是否执行，何时被执行以及是怎么被执行的。系统支持命令的撤消。

问题：

Need to issue requests to objects without knowing anything about the operation being requested or the receiver of the request.

意图：

• Encapsulate a request as an object, thereby letting you parameterize clients with different requests, queue or log requests, and support undoable operations.
• Promote “invocation of a method on an object” to full object status
• An object-oriented callback

责任链模式，个人感觉就是一个有序的协作模式，（PS:不知道无序的协作模式可不可以算做是责任链模式）

责任链模式 Chain

在责任链模式中，很多对象由每一个对象对其下家的引用而接起来形成一条链。请求在这个链上传递，直到链上的某一个对象决定处理此请求。客户并不知道链上的哪一个对象最终处理这个请求，系统可以在不影响客户端的情况下动态的重新组织链和分配责任。处理者有两个选择：承担责任或者把责任推给下家。一个请求可以最终不被任何接收端对象所接受。

问题：

There is a potentially variable number of “handler” or “processing element” or “node” objects, and a stream of requests that must be handled. Need to efficiently process the requests without hard-wiring handler relationships and precedence, or request-to-handler mappings.

意图：

• 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.
• Launch-and-leave requests with a single processing pipeline that contains many possible handlers.
• An object-oriented linked list with recursive traversal.

看名字就知道是干嘛的了。

代理模式 Proxy

看名字就能开解了。就是A可以访问B不能访问C，B能访问C，所以B把A的请求给C，把C的响应给A，顺便加点广告什么的，跳墙、VPN之类的都是如此。

问题：

You need to support resource-hungry objects, and you do not want to instantiate such objects unless and until they are actually requested by the client.

意图：

• 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.
• Wrap a complicated subsystem with a simpler interface

运用共享技术有效的支持大量细粒度的对象。 有点像对象可以变的单例。

享元模式 Flyweight

问题：

Designing objects down to the lowest levels of system “granularity” provides optimal flexibility, but can be unacceptably expensive in terms of performance and memory usage.

意图：

• Use sharing to support large numbers of fine-grained objects efficiently.
• The Motif GUI strategy of replacing heavy-weight widgets with light-weight gadgets.

这是任何编程里面使用最多的一个模式了!只要有松耦合思想，就有外观模式！

外观模式 Facdade

为子系统中的一组接口提供一个一致的界面，外观模式定义了一个高层接口，这个接口使得这一子系统更加容易使用。。

问题：

A segment of the client community needs a simplified interface to the overall functionality of a complex subsystem.

意图：

• 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.
• Wrap a complicated subsystem with a simpler interface

装饰模式是在不必改变原类文件和使用继承的情况下，动态地扩展一个对象的功能。它是通过创建一个包装对象，也就是装饰来包裹真实的对象

装饰模式 Decorator

问题：

You want to add behavior or state to individual objects at run-time. Inheritance is not feasible because it is static and applies to an entire class..

意图：

• Attach additional responsibilities to an object dynamically. Decorators provide a flexible alternative to subclassing for extending functionality.
• Client-specified embellishment of a core object by recursively wrapping it.
• Wrapping a gift, putting it in a box, and wrapping the box.

将对象组合成树形结构以表示“部分-整体”的层次结构。“组合” 使得用户对单个对象和组合对象的使用具有一致性,对于乘积比较复杂的数据结构使用。

组合模式 composite

问题：

Application needs to manipulate a hierarchical collection of “primitive” and “composite” objects. Processing of a primitive object is handled one way, and processing of a composite object is handled differently. Having to query the “type” of each object before attempting to process it is not desirable.

意图：

• Compose objects into tree structures to represent whole-part hierarchies. Composite lets clients treat individual objects and compositions of objects uniformly.
• Recursive composition
• “Directories contain entries, each of which could be a directory.”
• 1-to-many “has a” up the “is a” hierarchy.

经常使用到正则，没想到都这么熟了有时候还要翻资料，这里小小记录下下。

正则并不难，关键是多练，其实老实来说正则的性能并不是很高，关键是多练。以下要背熟于心，不要给我说用到的时候再百度一下什么的：

上面只是最最最基本的，最常用的，想用点高级功能可以再去找资料。这里给点示例代码

先是javaScript里面使用正则

//场景1：只需要得到是否匹配，使用test
var result = /MSIE [\w.]+/.test('Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; BTRS124307)');
if(result ){
    alert('ie');
}
else{
    alert('不匹配');
}

//场景2：除了要知道是否匹配，还要提出字符串
var result = /(MSIE) ([\w.]+)/.exec('Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; BTRS124307)');
if(result ){
    console.log(result[1]);
    console.log(result[2]);
}else{
    alert('不匹配');
}