1. class Animal {}
   
2. class Dog extends Animal{}
   
3. class Cat extends Animal{}
   
4. class GenericDemo {
   
5. public static void main(String[] args) {
   
6. Collection<Object> c = new ArrayList<Object>();
   
7. Collection<Animal> c1 = new ArrayList<Animal>();
   
8. Collection<Animal> c2 = new ArrayList<Dog>();
   
9. Collection<Animal> c3 = new ArrayList<Cat>();
   
10. 
    
11. Collection<? extends Animal> c4 = new ArrayList<Object>();
    
12. Collection<? extends Animal> c5 = new ArrayList<Animal>();
    
13. Collection<? extends Animal> c6 = new ArrayList<Dog>();
    
14. Collection<? extends Animal> c7 = new ArrayList<Cat>();
    
15. 
    
16. Collection<? super Animal> c8 = new ArrayList<Object>();
    
17. Collection<? super Animal> c9 = new ArrayList<Animal>();
    
18. Collection<? super Animal> c10 = new ArrayList<Dog>();
    
19. Collection<? super Animal> c11 = new ArrayList<Cat>();
    
20. }
    
21. }

复制代码

我可以说我看不懂吗。。。

c4  c10 c11非法的

泛型的上下限

表示不懂,等大神解读