what is the difference between required and Provided interfaces ?

On the implmentation level a provided interface is the interface implemented by a class (in the most common sense, e.g. a class B implements the interface I). Required interface would be any use of an interface by a component (e.g. if a class A defines a method that has the interface I as a parameter, this means that class A has a required interface I).

required属于A的变量
provided属于A实现的接口
required也用在方法的参数里

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