Video 9.5

Given that a Student is a Person, which of the following objects can be created?

• obj2 & obj4

• obj1, obj2, obj4

• All of these are valid

• 
  

  obj2, obj3, obj4

Answer explanation

Polymorphism works in this format: Superclass myVariable = new Subclass();

Clothing j = new Jeans(); // This works because all Jeans are Clothing

Jeans c = new Clothing(); // This doesn't work because not all Clothing is Jeans

Given that the Student class and the Worker class both extend from the Person class, what types of objects could be stored to the following array?

Person[] people = new Person[10];

• Only Person objects

• Student or Worker or Person objects, but not all three

• Student, Worker, and Person objects

Given that a MixedDog is a Dog, what is the correct way to create an array list to store both MixedDog objects and Dog objects?

• ArrayList<Dog> dogs = new ArrayList<Dog>();

• ArrayList<Dog> dogs = new ArrayList<MixedDog>();

• ArrayList<MixedDog> dogs = new ArrayList<Dog>();

• 
  

  ArrayList<MixedDog> dogs = new ArrayList<MixedDog>();