This chapter discusses abstract classes and interfaces in Java. It explains that abstract classes can contain abstract and concrete methods, where abstract methods have no body and must be overridden in subclasses. Interfaces are similar to abstract classes but can only contain method signatures without bodies that implementing classes must define. The chapter also covers polymorphism, casting, invoking superclass methods, and using interfaces.

1. Head First Java Chapter 8
Tom Henricksen

2. Abstract Class
abstract class Canine extends Animal {
public void roam() {}
}
Dog class extends Canine {

3. Abstract vs Concrete
● Abstract
○ Canine canine = new Canine();
● Concrete
○ Dog dog = new Dog();

4. Abstract methods
● No body
● Must override
public abstract void eat();

5. java.lang.Object
● Extend Object
● Basic methods
● Can instantiate
○ Object o = new Object();

6. Object overuse
ArrayList<Object> list = new ArrayList<Object>();
list.add(dog);
Dog dog2 = list.get(0);

7. Method calls
● Reference type
○ Dog dog = new Dog();
○ Object o = dog;
○ o.bark();

8. Use your methods
● Object methods
● Polymorphism
○ Snowboard s = new Snowboar();
○ Object o = s;

9. Casting
● Cast back
○ Dog d = (Dog)o;
○ d.bark();
● Instanceof

10. Interface
● Similar to an abstract class
○ public interface Pet {...}
○ public Dog implements Pet {...}

11. Interface methods
● No body
○ void play();
● Must implement

12. Invoking the Superclass
void runReport() {
super.runReport();
}

13. Assignment
● Exercise 1
● Exercise 2
● Exercise 3

14. Interfaces

15. Interfaces

16. Interfaces

17. Super