Understanding the use of generics in java

Question

Im trying to understand how class generics work and this bit just doesnt make sense to me.

So for instance if I have the following classes:

class A&l         


        

Answer 1

When you declare

A a1 = new A();

the compiler knows only that a1's type parameter is A or some subclass thereof--it doesn't know which one.

If you change it to A a1, then it will know that an instance of A is a legal argument. The same applies for a2.

On a related note, the line

class B extends A

uses a raw type. You should instead say Class B extends A or Class B extends A.