Question

Possible Duplicate:
Implementations and Collections

My super class is Exam. One of my sub classes is Analytical.

This is a valid within my ide

Exam object = new Analytical();

However this is not.

ArrayList<Exam> object = new ArrayList<Analytical>();

The error is from new to the end of the statement and it says “Change type of object to ArrayList. So my question is how can I properly utilize polymorphis with this data structure. Thank you.

Answer 1

You cannot have different parameterized types on two sides of generic type declaration..

So, you must use the same type on both side..

It should be: –

ArrayList<? extends Exam> object = new ArrayList<Analytical>();

or

ArrayList<Exam> object = new ArrayList<Exam>();

or

ArrayList<? extends Exam> object = new ArrayList<Exam>();

Polymorphism, does not apply on the parameterized type..