Container exercise 5, finished
Exercise 5: (3) Modify ListFeatures.java so that it uses Integers (remember
autoboxing!) instead of Pets, and explain any difference in results. One more question, why Arrays.asList() can return a fixed array
* Answer: Arrays.asList() use ArrayList inner class
* There is a difference between int and Integer, when add int type to ArrayList, we need a Integer object, not int primitive, so if use container, do not use primitive, use object, this is similar with generic