单件模式
特点:
1:单例类只能有一个实例。
2:单例类必须自己创建自己的唯一实例。
3:单例类必须给所有其它对象提供这一实例。
应用:
每台计算机可以有若干个打印机,但只能有一个Printer Spooler,避免两个打印作业同时输出到打印机。
一个具有自动编号主键的表可以有多个用户同时使用,但数据库中只能有一个地方分配下一个主键编号。否则会出现主键重复。
代码实现:
![](/Images/OutliningIndicators/None.gif)
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代码
![](/Images/OutliningIndicators/ExpandedBlockStart.gif)
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![](/Images/OutliningIndicators/None.gif)
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![](/Images/OutliningIndicators/InBlock.gif)
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![](/Images/OutliningIndicators/None.gif)
![](/Images/OutliningIndicators/None.gif)
![](/Images/OutliningIndicators/ExpandedBlockStart.gif)
![](/Images/OutliningIndicators/InBlock.gif)
![](/Images/OutliningIndicators/InBlock.gif)
![](/Images/OutliningIndicators/InBlock.gif)
![](/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
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![](/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
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![](/Images/OutliningIndicators/None.gif)
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特别提醒的是由于静态方法是线程共享的所以数据库连接字符串不能是静态类型.