To facilitate this, the plug-in class implements the singleton pattern: It stores a reference to itself in a private class variable.

为了使这一点更方便，插件类实现单模式（singleton pattern）：它在私有类变量中存储一个自身的引用。

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Unless the Settings wrapper class is designed using the singleton pattern, there can be multiple instances of the same application Settings class in a single application.

除非使用单一实例模式来设计设置包装类，否则单个应用程序中可能存在同一个应用程序设置类的多个实例。

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The Singleton pattern is shown in Figure 5.

Singleton模式如图5所示。

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