제네릭은 불공변

• java generic wildcards https://docs.oracle.com/javase/tutorial/java/generics/wildcards.html
• java Non-generic Vs Generic Collection https://www.geeksforgeeks.org/non-generic-vs-generic-collection-in-java/
• java generic_various http://tcpschool.com/java/java_generic_various
• java generic 가변인수 같이쓸때 주의할점 https://sejoung.github.io/2019/01/2019-01-07-Combine_generics_and_varargs_judiciously/#%EC%95%84%EC%9D%B4%ED%85%9C-32-%EC%A0%9C%EB%84%A4%EB%A6%AD%EA%B3%BC-%EA%B0%80%EB%B3%80%EC%9D%B8%EC%88%98%EB%A5%BC-%ED%95%A8%EA%BB%98-%EC%93%B8~~~~~~-%EB%95%8C%EB%8A%94-%EC%8B%A0%EC%A4%91%ED%95%98%EB%9D%BC