窥视设计模式之组合模式(composite)
经常使用Control,会发现Control有Controls的属性,而Controls集合包含的还是一个Control,类似的还有XmlNode.他们都有一个共有的特性,数据结构都是树行结构,什么是树形模式呢?
树(Tree)是n(n≥0)个结点的有限集T,T为空时称为空树,否则它满足如下两个条件:
(1) 有且仅有一个特定的称为根(Root)的结点;
(2) 其余的结点可分为m(m≥0)个互不相交的子集Tl,T2,…,Tm,其中每个子集本身又是一棵树,并称其为根的子树(SubTree)。上面给出的递归定义刻画了树的固有特性:一棵非空树是由若干棵子树构成的,而子树又可由若干棵更小的子树构成。而这里的子树可以是叶子也可以是分支。
先看下一幅图,里面的套娃就是一个套着一个的
这样一堆娃娃,一个大的套一个小的,小的里面还可以套更小的,所以其组织结构为:
Top Toy
- Toy
-- toy
----toy
----toy
如果用程序来描述上图,用设计模式的组合模式(Composite)是一个不错的主意
组合模式在GOF中定义为: 组合(Composite)模式将对象以树形结构组织起来,以达成“部分-整体”的层次结构,使得客户端对单个对象和组合对象的使用具有一致性。
类图为:
可以说,组合模式是比较简单易学的设计模式,我按照其定义和规则,实现一个论坛主题,帖子的组合关系
论坛中,一个主题可以包括很多帖子 ,一个帖子还可以包括很多回复。关系是:
Thread
-- Thread||Message
-- Thread||Message
下面是实现文件:
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工厂类为:
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客户端调用方法为:
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类关系图:
输结果为:
通过该事例的调用,就可以知道,组合模式的好处有:
1) 使客户端调用简单,客户端可以一致的使用组合结构或其中单个对象,用户就不必关心自己处理的是单个对象还是整个组合结构,这就简化了客户端代码。
2) 更容易在组合体内加入对象部件. 客户端不必因为加入了新的对象部件而更改代码。这一点符合开闭原则的要求,对系统的二次开发和功能扩展很有利!
出处:http://jillzhang.cnblogs.com/
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