關於泛型? extends T和？ super T

https://www.cnblogs.com/zhaoyibing/p/9051428.html

public class TestArrayList {
   public static void main(String[] args) {
       List<? super Animal> animal = new ArrayList<Animal>();
       animal.add( new Dog() );
       //Object a= animal.get( 0 );
       Dog a1 = (Dog) animal.get( 0 );
       a1.dog();

測試狗

Process finished with exit code 0

<? extends T>只能讀取無法儲存。 <? super T> 能儲存，並讀取，只是讀取時會喪失原類型，需要強轉。