For a class I was assigned to write code to read objects of the class Vehicle using ObjectInputStream (in). The objects are stored in an ArrayList called orders.

SSCE:

// Read all orders Object obj = in.readObject(); orders = (ArrayList<Vehicle>) obj; 

However, the compiler complains:

MacBook:Homework Brienna$   javac Orders.java -Xlint:unchecked Orders.java:152: warning: [unchecked] unchecked cast                     orders = (ArrayList<Vehicle>) in.readObject();                                                                 ^   required: ArrayList<Vehicle>   found:    Object 1 warning 

I always try to improve my code instead of ignoring or suppressing warnings. In this case, I have come up with a solution, but I’m trying to understand why it works, and if there is a better solution.

This update stops the warning:

// Read all orders, casting each order individually Object obj = in.readObject(); ArrayList ar = (ArrayList) obj; for (Object x : ar) {     orders.add((Vehicle) x); } 

Based on what I understand from what I’ve been reading, it works because (ArrayList<Vehicle>) obj may throw an exception if not all the elements are Vehicle. I am confused — non-Vehicle objects can be added to the ArrayList even if its type parameter has been specified as Vehicle? Also, is there a better solution, e.g. using instanceof?