C++ 策略模式

原文：http://blog.youkuaiyun.com/jarrettlife/article/details/51422040

策略模式定义： 
定义了算法家族，分别封装起来，让他们之间可以互相替换，此模式让算法的变化，不会影响到使用算法的客户。 
策略模式包含如下角色：

1. Context：环境类
2. Strategy：抽象策略类
3. ConcreteStrategy: 具体策略类

UML类图： 

测试用例

<code class="hljs lasso 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;">int main(){
    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//商品费用</span>
    double cost;
    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//采取某种收费策略之后的费用</span>
    double result;
    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//假如</span>
    cost <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1029.88</span>;

    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//声明要使用的具体策略类</span>
    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//这里显示出了策略类的缺点：客户端必须知道有哪些具体封装的算法。如本例必须知道三种收费方式Normal、Return、Rebate。</span>
    StrategyCashSuper <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">*</span>Normal <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">new</span> ConerectStrategyNormal(cost);<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//抽象策略类（基类）指针指向派生类->具体策略类（普通收费方式）</span>
    StrategyCashSuper <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">*</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">Return</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">new</span> ConerectStrategyReturn(cost); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//满300返100收费方式</span>
    StrategyCashSuper <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">*</span>Rebate <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">new</span> ConerectStrategyRebate(cost); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//打八折收费</span>
    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//声明环境类，具体调用的算法，由它来维护</span>
    Context <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">*</span>c <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">new</span> Context();
    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//设置使用的策略类</span>
    c<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">-></span>setStrategy(Normal);<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//设置为普通收费</span>
    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//调用算法</span>
    result <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> c<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">-></span>getChargeResult();
    std<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;">::cout</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><<</span> <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Accrued expenses: "</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><<</span> result <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><<</span> std<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;">::endl</span>;

    c<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">-></span>setStrategy(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">Return</span>);<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//设置为满300返100收费方式</span>
    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//调用算法</span>
    result <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> c<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">-></span>getChargeResult();
    std<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;">::cout</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><<</span> <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Accrued expenses: "</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><<</span> result <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><<</span> std<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;">::endl</span>;

    c<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">-></span>setStrategy(Rebate);<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//设置为打八折收费</span>
    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//调用算法</span>
    result <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> c<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">-></span>getChargeResult();
    std<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;">::cout</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><<</span> <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Accrued expenses: "</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><<</span> result <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><<</span> std<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;">::endl</span>;

    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</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><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><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li></ul>

头文件Strategy.h

<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-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#ifndef _2STRATEGY_H_</span>
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#<span class="hljs-keyword" style="box-sizing: border-box;">define</span> _2STRATEGY_H_</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//策略类，算法基类</span>
class StrategyCashSuper{
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">protected</span>:
    //商品应付费用，定义为保护成员供子类继承
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">double</span> cost;   
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span>:
    //构造函数
    <span class="hljs-title" style="box-sizing: border-box;">StrategyCashSuper</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">double</span> c):<span class="hljs-title" style="box-sizing: border-box;">cost</span>(c){}
    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//收费结果算法</span>
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">virtual</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">double</span> ChargeResult();<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//本想定义为纯虚函数，但不可以。因为虚基类本不能实例化</span>
};

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//正常收费算法</span>
class ConerectStrategyNormal: <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> StrategyCashSuper{
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span>:
    //构造函数
    <span class="hljs-title" style="box-sizing: border-box;">ConerectStrategyNormal</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">double</span> c):<span class="hljs-title" style="box-sizing: border-box;">StrategyCashSuper</span>(c){}
    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//根据本类的收费方式，重写继承的收费算法</span>
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">double</span> ChargeResult()<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">override</span>;
};

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//满300返100收费算法</span>
class ConerectStrategyReturn: <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> StrategyCashSuper{
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span>:
    //构造函数
    <span class="hljs-title" style="box-sizing: border-box;">ConerectStrategyReturn</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">double</span> c):<span class="hljs-title" style="box-sizing: border-box;">StrategyCashSuper</span>(c){}
    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//重写收费算法</span>
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">double</span> ChargeResult()<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">override</span>;    
};

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//打八折收费算法</span>
class ConerectStrategyRebate: <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> StrategyCashSuper{
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span>:
    //构造函数
    <span class="hljs-title" style="box-sizing: border-box;">ConerectStrategyRebate</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">double</span> c):<span class="hljs-title" style="box-sizing: border-box;">StrategyCashSuper</span>(c){}
    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//重写收费算法</span>
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">double</span> ChargeResult()<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">override</span>;  

};

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//环境类，根据具体算法，维护上下文使用的类</span>
class Context{
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span>:
    //策略基类
    StrategyCashSuper *SCS;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span>:
    //设置使用的策略
    <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;">setStrategy</span>(StrategyCashSuper *s);
    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//具体执行的算法</span>
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">double</span> getChargeResult();
};

<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#<span class="hljs-keyword" style="box-sizing: border-box;">endif</span></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><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><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li><li style="box-sizing: border-box; padding: 0px 5px;">52</li><li style="box-sizing: border-box; padding: 0px 5px;">53</li><li style="box-sizing: border-box; padding: 0px 5px;">54</li><li style="box-sizing: border-box; padding: 0px 5px;">55</li></ul>

实现Strategy.cpp

<code class="hljs lasso 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-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">#include</span> <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"2Strategy.h"</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//基类</span>
double StrategyCashSuper<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;">::ChargeResult</span>(){
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;
}

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//正常收费</span>
double ConerectStrategyNormal<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;">::ChargeResult</span>(){
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> cost;
}

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//满300返100收费算法</span>
double ConerectStrategyReturn<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;">::ChargeResult</span>(){
    double res <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> cost;
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span>(res <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">>=</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">300</span>)
        res <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> cost <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">-</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">100</span>;
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> res;
}
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//打八折收费算法</span>
double ConerectStrategyRebate<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;">::ChargeResult</span>(){
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> cost <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">*</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0.8</span>;
}

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//设置使用的算法</span>
<span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">void</span> Context<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;">::setStrategy</span>(StrategyCashSuper <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">*</span>s){
    SCS <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> s;
}

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//具体执行的算法</span>
double Context<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;">::getChargeResult</span>(){
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> SCS<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">-></span>ChargeResult();
}</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><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li></ul>

总结：

1. 策略模式让算法独立于使用它的客户而变化，也成为政策模式。策略模式是一种对象行为型模式。
2. 策略模式包含3个角色：抽象策略类为所支持的算法声明了抽象方法，是所有策略类的父类；具体策略类实现了在抽象策略类中定义的算法。环境类在解决某个问题时可以采用多种策略类（缺点是客户端需要知道所有封装的策略类），在环境类中维护一个对抽象策略类的引用实例。
3. 策略模式是对算法的封装，它把算法的责任和算法本身分割开，委派给不同的对象管理。策略模式通常把一个系列的算法封装到一系列的策略类里面，作为一个抽象策略类的子类。
4. 策略模式主要优点在于对“开闭原则”的完美支持，在不修改原有系统的基础上可以更换算法或者增加新的算法，它很好的管理算法家族，提高了代码的复用性，是一种替换继承，避免多重条件转移语句的实现方式；其缺点在于客户端必须知道所有的策略类，并理解其区别，同时在一定程度上增加了系统中类的个数，可能会存在很多策略类。
5. 策略模式适用情况包括：在一个系统里面有许多类，它们之间的区别仅在于它们的行为，使用策略模式可以动态地让一个对象在许多行为中选择一种行为；一个系统需要动态地在几种算法中选择一种；避免使用难以维护的多重条件选择语句；希望在具体策略类中封装算法和与之相关的数据结构。

顶

1