Questions

• Reading?
• Quiz?
• Homework?

Activity - super class and subclass

Record your participation in Piazza clicker question Lesson24 Q1

Think about the Product and Toy classes from last lesson. Toy is a subclass of Product. product and littlePeople are defined as:

  Product product = new Product(....);
  Toy littlePeople = Toy(....);
  

Which of the following calls are legal? (May be multiple answers)

1. product.getPrice()
2. littlePeople.getPrice()
3. product.getAppropriateAge()
4. littlePeople.getAppropriateAge()

Polymorphism

• Polymorphism means "many forms"
• In Java you can assign a subclass object to a super class reference variable
• Which method is called is always determined by the type of the actual object, not the type of object reference variable
  • This is called late binding or dynamic look-up
• Let's see what this means

Activity - Polymorphism in action

Record your participation in Piazza clicker question Lesson24 Q2

• Download toy_polymorphism.zip
• In ToyTester, declare a Product object reference variable myProduct and assign rocket to it.

  Product myProduct = rocket;

• Will it compile? Why?
• Add System.out.println( myProduct.getAppropriateAge()). What happens?
• In ToyTester add

  Product watch = new Product("Apple Watch", 300.00); 

• Create a Product array that will hold 2 items
• Assign the watch at index 0 and the rocket at index 1.
• Will it compile? Why or why not?
• Use an enhanced for loop to print the description of each item
• Run it
• What do you notice?
• Which method is executed is determined at run time - not compile time

 

Activity - Object reference variable

Record your participation in Piazza clicker question Lesson24 Q3

If we add this code to the ToyTester,

   Product thing = rocket;
   System.out.println(thing.getAppropriateAge());

will it compile?

1. Yes
2. No
3. I have no idea

Activity - Object reference variable

Record your participation in Piazza clicker question Lesson24 Q4

Which of the following method calls are valid, given the declarations in ToyTester. Check all that are valid

1. rocket.increasePrice(10)
2. thing.increasePrice(10)
3. rocket.getDescription()
4. thing.getDescription()
5. rocket.getAppropriateAge()
6. thing.getAppropriateAge()

 

 

Activity - Casting

Record your participation in Piazza clicker question Lesson24 Q5

You have a Product object reference, thing. thing actually references a Toy object (rocket). You want to know the appropriate age. How can you get it?