《Android源码设计模式解析与实战》读书笔记(二十二)
2016-05-05 16:22
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http://blog.csdn.net/qq_17766199/article/details/50534726
第二十二章、享元模式
享元模式是结构型设计模式之一,是对对象池的一种实现。就像它的名字一样,共享对象,避免重复的创建。我们常用的String就是使用了共享模式,所以
String类型的对象创建后就不可改变,如果当两个
String对象所包含的内容相同时,JVM只创建一个
String对象对应这两个不同的对象引用。
1.定义
采用一个共享来避免大量拥有相同内容对象的开销。使用享元模式可有效支持大量的细粒度对象。
2.使用场景
(1)系统中存在大量的相似对象。(2)细粒度的对象都具备较接近的外部状态,而且内部状态与环境不关,也就是说对象没有特定身份。
(3)需要缓冲池的场景。
PS:内部状态与外部状态:在享元对象内部并且不会随着环境改变而改变的共享部分,可以称之为享元对象的内部状态,反之随着环境改变而改变的,不可共享的状态称之为外部状态。
3.UML类图
享元模式分为单纯享元模式和复合享元模式,上图是复合享元模式。
(1)
Flyweight:享元对象抽象基类或者接口。
(2)
ConcreateFlyweight:具体的享元对象,如果有内部状态的话,必须负责为内部状态提供存储空间。
(3)
UnsharadConcreateFlyweight:复合享元角色所代表的对象是不可以共享的,并且可以分解成为多个单纯享元对象的组合。单纯享元模式没有此项,这也是两者在结构上的区别。
(4)
FlyweightFactoiy:享元工厂,负责管理享元对象池和创建享元对象。
(5)
Client:维护对所有享元对象的引用,而且还需要存储对应的外蕴状态。
4.简单实现
情景:过年买火车票的时候,我们需要查询车票的情况,那么如果每次查询车票时都创建一个结果,那么必然会大量的创建出许多重复的对象,频繁的去销毁他们,使得GC任务繁重。那么这时我们可以使用享元模式,将这些对象缓存起来,查询时优先使用缓存,没有缓存在重新创建。首先是Ticket接口(Flyweight):
<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">interface</span> Ticket { <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">showTicketInfo</span>(String bunk); } </code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li></ul>
TrainTicket具体实现类(ConcreateFlyweight):
<code class="hljs java has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//火车票</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">TrainTicket</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">implements</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">Ticket</span>{</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> String from; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 始发地</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> String to; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 目的地</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> String bunk; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//铺位</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> price; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//价格</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-title" style="box-sizing: border-box;">TrainTicket</span>(String from, String to) { <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>.from = from; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>.to = to; } <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">showTicketInfo</span>(String bunk) { price = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Random().nextInt(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">300</span>); System.out.println(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"购买 从 "</span> + from + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">" 到 "</span> + to + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"的"</span> + bunk + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"火车票"</span> + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">", 价格:"</span> + price); } } </code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li></ul>
TicketFactory 管理查询火车票(FlyweightFactoiy):
<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> TicketFactory { <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> Map<String, Ticket> sTicketMap = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> ConcurrentHashMap<String, Ticket>(); <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> Ticket <span class="hljs-title" style="box-sizing: border-box;">getTicket</span>(String <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">from</span> ,String to){ String key = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">from</span> + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"-"</span> + to; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span>(sTicketMap.containsKey(key)){ System.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">out</span>.println(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"使用缓存 ==> "</span> + key); <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> sTicketMap.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">get</span>(key); }<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span>{ System.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">out</span>.println(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"创建对象 ==> "</span> + key); Ticket ticket = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> TrainTicket(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">from</span>, to); sTicketMap.put(key, ticket); <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> ticket; } } }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li></ul>
查询:
<code class="hljs java has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> class Client { <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">main</span>(String[] args) { Ticket ticket01 = TicketFactory.getTicket(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"北京"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"青岛"</span>); ticket01.showTicketInfo(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"上铺"</span>); Ticket ticket02 = TicketFactory.getTicket(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"北京"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"青岛"</span>); ticket02.showTicketInfo(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"下铺"</span>); Ticket ticket03 = TicketFactory.getTicket(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"北京"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"西安"</span>); ticket03.showTicketInfo(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"坐票"</span>); } } </code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li></ul>
结果
<code class="hljs php has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">创建对象 ==> 北京-青岛 购买 从 北京 到 青岛的上铺火车票, 价格:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">71</span> 使用缓存 ==> 北京-青岛 购买 从 北京 到 青岛的下铺火车票, 价格:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">32</span> 创建对象 ==> 北京-西安 购买 从 北京 到 西安的坐票火车票, 价格:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">246</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li></ul>
5.Android源码中的实现
1.Message
因为Android是事件驱动的,因此如果通过new创建 Message就会创建大量的
Message对象,导致内存占用率高,频繁GC等问题。那么
Message就采用了享元模式。
Message通过
next成员变量保有对下一个
Message的引用,最后一个可用
Message的
next则为空。从而构成了一个Message链表。
Message Pool就通过该链表的表头管理着所有闲置的
Message,一个
Message在使用完后可以通过
recycle()方法进入
Message Pool,并在需要时通过
obtain静态方法从
Message Pool获取。
Message承担了享元模式中3个元素的职责,即是
Flyweight抽象,又是
ConcreateFlyweight角色,同时又承担了
FlyweightFactoiy管理对象池的职责。
所以使用Message推荐obtain(),不要去new了。
<code class="hljs mathematica has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">//<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>。使用new <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">Message</span>() //<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">Message</span> mess = new <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">Message</span>(); //<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>。使用<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">Message</span>.obtain() <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">Message</span> mess = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">Message</span>.obtain(); mess.what = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>; //<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">Message</span> mess = mHandler.obtainMessage(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>); 与上两行的代码一样,可以参考源码查看 mHandler.sendMessage(mess); </code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li></ul>
6.总结
1.优点
(1)大大减少应用程序创建的对象,降低程序内存的占用,增强程序的性能。(2)使用享元模式,可以让享元对象可以在不同的环境中被共享。
2.缺点
(1)使得系统更加复杂。为了使对象可以共享,需要将一些状态外部化,这使得程序的逻辑复杂化。(2)享元模式将需、享元对象的状态外部化,而读取外部状态使得运行时间稍微变长。
7.参考
1. 深入浅出享元模式
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