The hierarchy of the type XXXX is inconsistent

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These errors happend because some  interface /class in the hierarchy cannot be resolve.
For example: the error is occur in your class - class x, x inherits y, and in turn, y inherits z. However, the  compiler

cannot resolve z (in above error is EventManager), because z is belong to a library that is not included.
Therefore, you have to add package containing z to the classpath/ or project's   Java   Build Path (if you are using eclipse).