Class 22: Interfaces

Held: Tuesday, February 28, 2006

Summary: Today we consider how Java's interfaces allow us to separate the general capabilities of our classes from the particular implementations we choose.

Related Pages:

• EBoard.
• Espresso: Separating the How from the What with Java Interfaces.
• Espresso: Lab on Java Interfaces.

Assignments

• Read Espresso: Reusing and Generalizing Code, Part 1: Polymorphism in Java.

Notes:

• I will reserve time for questions on the exam.

Overview:

• Background.
• Lab.

Background

• As I've told you a few times, one of the key ideas in object-oriented programming is encapsulation.
• When we encapsulate an object, we limit the access a client of an object has to the internals of an object.
• Similarly, when we design (and document) a method, we tell the client what the method does and little about how the method does what it does.
• Interfaces provide another level of abstraction.
• An interface describes only the what of an object.
• A separate class (or, more importantly, multiple classes) describe the how.

Lab

• Questions?
• Do the lab.
• Reflection?