仅在子类型扩展的类有一个可访问的无参数构造方法来初始化该类的状态时，才可以假定子类型有此职责。
The subtype may assume this responsibility only if the class it extends has an accessible no-arg constructor to initialize the class's state.
信任管理是一种具有动态可扩展性的新型访问控制方法。
Trust management is a new kind of access control method which is dynamic and scalable.
信任管理是一种具有动态可扩展性的新型访问控制方法。
Trust management is a new kind of access control method which is dynamic and scalable.
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