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).