Which of the following code snippets is VALID regarding the use of a parent (superclass) reference for holding objects of its child class?Group of answer choicesAnimal animal = new Dog();List<Animal> animalList = new ArrayList<Animal>();animalList.add(new Dog());Animal animal = new Dog();List<Dog> dogList = new ArrayList<Animal>();Animal animal = new Dog();List<Dog> dogList = new ArrayList<Dog>();dogList.add(new Animal());Animal animal = new Dog();List<Animal> animalList = new ArrayList<Dog>();
Question
Which of the following code snippets is VALID regarding the use of a parent (superclass) reference for holding objects of its child class?Group of answer choicesAnimal animal = new Dog();List<Animal> animalList = new ArrayList<Animal>();animalList.add(new Dog());Animal animal = new Dog();List<Dog> dogList = new ArrayList<Animal>();Animal animal = new Dog();List<Dog> dogList = new ArrayList<Dog>();dogList.add(new Animal());Animal animal = new Dog();List<Animal> animalList = new ArrayList<Dog>();
Solution
The valid code snippet is:
Animal animal = new Dog();
List<Animal> animalList = new ArrayList<Animal>();
animalList.add(new Dog());
Explanation:
In Java, a reference variable of a superclass can be used to hold the object of its subclass. So, Animal animal = new Dog(); is valid.
List<Animal> animalList = new ArrayList<Animal>(); is also valid because we are creating an ArrayList that can hold Animal objects.
animalList.add(new Dog()); is valid because a Dog is an Animal, so we can add a Dog to a list of Animals.
The other code snippets are not valid because:
-
List<Dog> dogList = new ArrayList<Animal>();is not valid because we cannot assign an ArrayList of Animals to a reference of ArrayList of Dogs. -
dogList.add(new Animal());is not valid because we cannot add an Animal to a list of Dogs. A Dog is an Animal, but an Animal is not necessarily a Dog. -
List<Animal> animalList = new ArrayList<Dog>();is not valid because we cannot assign an ArrayList of Dogs to a reference of ArrayList of Animals.
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