Variables with wildcard

Question

hi,
can some explain following code.what is the difference between these 3 variables.
List<? extends Animal> li1= new ArrayList<Animal>();
List<? super Animal> li2= new ArrayList<Animal>();
List<?> li3= new ArrayList<Animal>();
Edited by: dvrajitha on Oct 10, 2007 3:28 AM

Answer 1

Consider this Object hierarchy:
Object > Lifeform > Animal > Canine > Lupine
And this simple case:
List<Animal> li0 = new ArrayList<Animal>();
li0 can only be assigned a List of Animal
li0 cannot be assigned a List of Object, Lifeform, Canine, or Lupine.
li1 can be assigned a List of Animal, or its subclasses Canine, or Lupine
li1 cannot be assigned a List of Object or Lifeform.
li2 can be assigned a List of Animal or its superclasses, Lifeform and Object
li2 cannot be assigned a List of Canine or Lupine.
li3 can be assigned a list of anything.
'? extendsT' sets an upper bound of T; values will either be T or some more specific class
'?super T' sets a lower bound of T; values will either be T or some more general class
Edited by: devon_c_miller on Oct 10, 2007 9:40 AM