wildcard type parameter

[Bob CHOI]

i wrote following code snippet for understanding "wildcard generic type", or i'd prefer to call it "wildcard type parameter".

pls comment whether i've got the essence behind the scenes. Thanks!

 
package mypkg;
import java.util.*;
 
class MyGenericTest {

 public static void main(String[] args) {

MyList<Animal> animalHouse = new MyList<Animal>(); //create the object of "BaseType<SuperType>"

MyList<Cat> catHouse = new MyList<Cat>(); //create the object of "BaseType<SubType>"
for (int i=0;i<10;i++) {
catHouse.seet(new Cat());
animalHouse.aadd(catHouse); //pass the object of "BaseType<SubType>" to "BaseType<SuperType>"
}

MyList<Dog> dogHouse = new MyList<Dog>(); //create the object of "BaseType<OtherSubType>"
for (int i=0;i<10;i++) {
dogHouse.seet(new Dog());
animalHouse.aadd(dogHouse); //pass the object of "BaseType<OtherSubType>" to "BaseType<SuperType>"
}
 
for(Animal animal:animalHouse.geet()) //retrieve the objects of mixed sub types
System.out.println(animal); 
 
}
 
}
 
class MyList<E extends Animal> {
 
private List<E> myList = new ArrayList<E>();
private E e = null;
 
void seet(E e) {
 
this.e = e;
 
}
 
void aadd(MyList<? extends E> myList) { //"wildcard generic type" or "wildcard type parameter" declaration to allow type parameter subcasting
 
this.myList.add(myList.e);
 
}
 
List<E> geet() {
 
return myList;
 
}
 
}
 
class Animal {}
 
class Cat extends Animal {}
 
class Dog extends Animal {}
 

(added

tags)
[ December 01, 2006: Message edited by: Barry Gaunt ]