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Java cannot be considered 100% object oriented is due to its existence of
primitive variables like int, long, char, float, etc.
Another reason why Java is considered not full object oriented is due to its existence of static methods and variables Since static methods can be invoked without instantiating an object, we could say that it breaks the rules of encapsulation.
Java does not support multiple class inheritance because different classes may have different variables with same name that may be contradicted and can cause confusions and result in errors. one can argue that Java is not 100% object oriented according to this point of view.