Questions

• Reading?
• Quiz?
• Homework?

Activity - super class and subclass

Record your participation in Piazza clicker question Lesson16 Q1

Think about the Product and Toy classes from last lesson. Toy is a subclass of Product. Assume product  is an object of the class Procuct and littlePeople is an object of the class 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 Lesson16 Q2

• Download toy_polymorphism.zip
• 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 Lesson16 Q3

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 Lesson16 Q4

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

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

Activity - Casting

Record your participation in Piazza clicker question Lesson16 Q5

You have a Product object reference, thing. thing actually references a Toy object (rocket). You want to know the appropriate age. What code can you use to do that?