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  1. import java.util.*;
  2. class Ideone
  3. {
  4. 	public static void main (String[] args) throws java.lang.Exception
  5. 	{
  6. 		List<Dog> dogs = new ArrayList<>();
  7. 		dogs.add(new Dog());
  8. 		dogs.add(new Dog());
  9.  
  10. 		// fun(dogs); // not allowed
  11.  
  12. 		List<Animal> animals = new ArrayList<>();
  13. 		animals.add(new Animal());
  14. 		animals.add(new Animal());
  15.  
  16. 		fun(animals);
  17.  
  18. 		fun2(dogs);
  19. 		fun2(animals);
  20.  
  21. 		fun3(animals);
  22. 		fun3(dogs);
  23. 	}
  24.  
  25. 	static void fun(List<Animal> animals){
  26. 		for(Animal a : animals){
  27. 			a.eat();
  28. 		}
  29. 	}
  30.  
  31. 	static void fun2(List<?> values){ // can only be read
  32. 		for(Object obj : values){
  33. 			System.out.println(obj.getClass());
  34. 		}
  35.  
  36. 		// values.add(new Animal()); // not allowed to modify in wildcard generics
  37. 	}
  38.  
  39. 	static void fun3(List<? extends Animal> values){ // wildcards with upper bound
  40. 		for(Animal a : values){
  41. 			a.eat();
  42. 		}
  43. 	}
  44. }
  45.  
  46. class Animal {
  47. 	void eat(){
  48. 		System.out.println("Animal eats");
  49. 	}
  50. }
  51.  
  52. class Dog extends Animal {
  53. 	void eat(){
  54. 		System.out.println("Dog eats");
  55. 	}
  56. 	void bark(){
  57. 		System.out.println("Dogs can bark");
  58. 	}
  59. }
Success #stdin #stdout 0.07s 52548KB
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Animal eats
Animal eats
class Dog
class Dog
class Animal
class Animal
Animal eats
Animal eats
Dog eats
Dog eats
https://ideone.com/DQalMj
language:
Java (HotSpot 12)
created:
1 hour ago
visibility:
public

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