#10 generics + wild card

Question 1

define a generic class

Answer 1

class MyGeneric
(any capital letter will do)

Question 2

instantiate something of a generic class type

Answer 2

ArrayList x = new ArrayList<>;

MyGeneric V;

Question 3

what types can be used in generic

Answer 3

reference types and wrapper

Question 4

before generics

Answer 4

objects had to be downcast when returned from library classes?

Question 5

can an arraylist of super class type hold subclass and superclass objects?

Answer 5

yes!

Question 6

bounded type parameter

Answer 6

class MyGeneric
(only vehicle or vehicle subclass types can be passed in)
(vehicle methods can be called from E references)

Question 7

if S is a subclass of T, is Generic a subclass of Generic ?

Answer 7

no, only if you add

Generic

Question 8

wild card parameter >

Answer 8

any unknown type!

Question 9

ArrayList extends Vehicle>

Answer 9

arraylist of any type Vehicle or subclass of vehicle

Question 10

ArrayList super Vehicle>

Answer 10

arraylist of any type Vehicle or superclass of vehicle

Question 11

when can wild card be used?

Answer 11

1. reference declaration
2. some method return vales
3. CANNOT instantiate objs

Question 12

element type of array cannot be type param of a generic class. what is the workaround?

Answer 12

array of object references and cast it to the generic type

causes unchecked cast so write
@SuppressWarnings(“unchecked”)