什么时候具体用到'单例模式'.

Ref:  stackoverflow

  We use single global LogManager  to maintain a set of shared state about Loggers and log services.

  • Manages a hierarchical namespace of Logger objects. All named Loggers are stored in this namespace.
  • Manages a set of logging control properties. These are simple key-value pairs that can be used by Handlers and other logging objects to configure themselves.

  Every Java application has a single instance of class Runtime that allows the application to interface with the environment in which the application is running. The current runtime can be obtained from the getRuntime method.

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