Interfaces, Polymorphism and Packages

April 13th, 2016

Slides

Lecture Recording

Lecture Code

• iShape
• Circle
• Square
• Triangle
• Package Example (zip)
• Package Example

Key Points

• public interface iName
• public class className implements iName
• In an interface, you can declare constants and then abstract methods
• Polymorphism occurs when one method behaves differently when called in the context of different class instances

Interfaces

• Interfaces provide a regimented list of methods that a certain class is obligated to provide. A class is obligated to provide them if it "implements" the interface.
• Think of an interface as a contract. If a class implements the interface, it is contractually bound to provide the methods listed in the interface.
• Interfaces enable teams of coders to work on two different sections of code, knowing that because the interface is agreed upon, their code will be compatible.
• link

Polymorphism

• Late binding: Resolving a specific method call on an object is done at runtime instead of compile time.
• Polymorphism: Allowing multiple implementations of the same method, where the specific method executed is chosen at runtime based on the actual object. link

Packages

• Packages are ways to divide and organize classes into logical groups.
• Packages are groups of classes that work together to accomplish a common task (further supports encapsulation).
• Packages make it easier to find and use classes as well as control access. link

Class Exercise

Declare an interface named iShape that has a method called getArea() that returns a double. Declare and demonstrate a Circle class that implements iShape. Declare and demonstrate a Square class that implements iShape.