ArrayList and List

[Heba Mahmoud]

  public class AnimalDoctorGeneric {
	
	
    public void  checkAnimals(ArrayList<Animal> animals) {
		for(Animal a : animals)
			a.checkUp();
	}
    
    public static void main(String[] args) {  
    	AnimalDoctorGeneric doc= new AnimalDoctorGeneric();
    	List<Animal> animals = new ArrayList<Animal>();
    	animals.add(new Dog());
    	animals.add(new Dog());
    	animals.add(new Dog());
    	[u]doc.checkAnimals(animals); [/u]
}
} 

why when passing to the method List<Animal> instead of ArrayList<Animal> it cause a complair error
The method checkAnimals(ArrayList<Animal>) in the type AnimalDoctorGeneric is not applicable for the arguments (List<Animal>)
although we can say List<Animal> a= new ArrayList<Animal>(); when declaring it.

[Henry Wong]

why when passing to the method List<Animal> instead of ArrayList<Animal> it cause a complair error
The method checkAnimals(ArrayList<Animal>) in the type AnimalDoctorGeneric is not applicable for the arguments (List<Animal>)
although we can say List<Animal> a= new ArrayList<Animal>(); when declaring it.

Because while all ArrayList<Animal> IS-A List<Animal> is true, which is why the assignment is legal, not all List<Animal> IS-A ArrayList<Animal>, which is why the method call is not legal.

Henry