Chapter 9: Interfaces and Polymorphism

Sample Interface

public interface Animal
{
  String getSound();
}

Sample Interface Implementation

public class Dog implements Animal
{
  public String getSound()
  {
    // whatever
  }

  // other parts of Dog class
}

public class Cat implements Animal
{
  public String getSound()
  {
    // whatever
  }

  // other parts of Cat class
}

Definitions

Polymorphism: the behavior of an object depends on the actual type of object.
When behavior is determined at run time, this illustrates late binding.
When behavior is determined at compile time, this illustrates early binding.

Converting Between Classes and Interfaces

Cat myCat = new Cat (...);
Dog myDog = new Dog (...);
Animal myPet;

myCat.getSound();     // early binding

myPet = myCat;        // conversion
myPet.getSound();     // polymorphism, late binding

myPet = myDog;        // conversion 
myPet.getSound();     // polymorphism, late binding

myDog = (Dog) myPet;  // conversion
myCat = (Cat) myPet;  // error, myPet is not currently a Cat

Chapter 9: Interfaces and Polymorphism

Sample Interface

Sample Interface Implementation

Definitions

Converting Between Classes and Interfaces

Lecture Code