Java Generics: The Difference between Java Arrays and Generic Lists | OneWebSQL

studentList = personList;

Answer: incorrect.
This one is obvious to anyone. Surely a list of Persons cannot be assigned to a variable containing a list of Students because the list can contain Person objects which are notStudents.

personList = studentList;

Answer: incorrect.
This assignment is not correct because List<Student> is not a subclass of List<Person>. This is surprising to many Java beginners. Here's an explanation. Imagine for a moment that the assignment was correct. Then the variable personList would hold a reference to thestudentList object (a list of Students). But the variable personList only knows that it is a list of Persons. One can try to insert a Professor into the list.

?

1	personList.add(new Professor("A","B")); //incorrect but compiles

The compiler does not know that the insert operation is incorrect. The runtime system has no way of knowing that the insert is incorrect. 

personArray = studentArray;

Answer: correct.
Here we have another surprise. Arrays in Java are covariant, which, in our example, means that if Student is a subclass of Person (which it is), then Student[] is a subclass ofPerson[].

Java arrays know the type of its elements and they check at runtime whether an element can be inserted into it.
it's not possible that an exception is thrown in a similar situation with parametrized lists. The generic lists do not know the type of its elements at runtime. They cannot checkwhether an element can be inserted into the list. As a consequence, List<Person> is not a subclass of List<Student>.
Read full article from Java Generics: The Difference between Java Arrays and Generic Lists | OneWebSQL