Generics - what does it mean "? super T"?

[Mateus Lucio]

Hi folks!
I understood what <? extends T> means that ? is subtype of T, in other words ? extends or implements T, but what about the super?
does it mean that ? is supertype of T??? I really didnt catch that!!!

I'd appreciate if you guys explained it to me!
thanks in advance!!

[Keith Lynn]

Yes, it means T or a superclass of T.

[Mateus Lucio]

By superclass you mean only extention (extends)? or it works for interfaces too?

by the way, if its not asking too much could give me an exemple of a situation where I'd take advantage of this?

[Keith Lynn]

Yes it also works for superinterfaces.

Here is an example of using the lower bounded wildcard.

import java.util.*;
 
interface Curlable {
 
   public void curl();
 
}
 
abstract class Animal {
 
   protected abstract String name();
 
}
 
class Dog extends Animal {
 
   public String name() {
      return("Dog");
   }
 
}
 
class Poodle extends Dog {
 
   public String name() {
      return("Poodle");
   }
 
}
 
class ShortHair extends Poodle implements Curlable {
 
   public String name() {
      return("ShortHair");
   }
 
   public void curl() {
      System.out.println("This shorthair poodle can be curled.");
   }
 
}
 
class Cat extends Animal {
 
   public String name() {
      return("Cat");
   }
 
}
 
public class Test {
 
   public static void addToList(List<? super ShortHair> list,
                                ShortHair shortHair) {
      list.add(shortHair);
   }
 
   public static void iterate(List<? extends Animal> list) {
      for (Animal animal : list)
         System.out.println(animal.name());
   }
 
   public static void iterateCurlable(List<? extends Curlable> list) {
      for (Curlable curlable : list)
         curlable.curl();
   }
      
   public static void main(String[] args) {
      List<Animal> list = new ArrayList<Animal>();
      List<Dog> list1 = new ArrayList<Dog>();
      List<Poodle> list2 = new ArrayList<Poodle>();
      List<Curlable> list3 = new ArrayList<Curlable>();
 
      addToList(list,new ShortHair());
      addToList(list1,new ShortHair());
      addToList(list2,new ShortHair());
      addToList(list3,new ShortHair());
 
      iterate(list);
      iterate(list1);
      iterate(list2);
      iterateCurlable(list3);
   }
 
}

[ November 08, 2006: Message edited by: Keith Lynn ]

[Mateus Lucio]

I see! ... thank you very much!
I understand it, now I'll write and run some code to master it (or be as close as possible)

Thanks again!

[zero Corner]

i am totally new in the Generic type in java, i don't really get what does the ? mean

public static <T extends Comparable<? super T>> void bubbleSort(T[] a, int n)

1)what does <T extends Comparable<? super T>> really mean? declaring the Generic T for the compiler to recognize it?
2) what does ? really for?

thank you in advance...

[Rob Spoor]

Zero Corner, you have been warned about your name twice before. This is your last warning. Change it to something appropriate or your account will be closed.