This document discusses abstract classes and interfaces in Java. It begins by defining an interface and how to declare methods in an interface. It then discusses how to implement an interface in a class. The document notes that unlike abstract classes, interfaces can only contain abstract methods and constants. It explains that interfaces allow for multiple inheritance in Java while abstract classes do not. The key differences between abstract classes and interfaces are summarized. Finally, it provides some guidelines on class design and recommends next steps for learning additional Java topics after understanding object-oriented programming fundamentals.

1. Chapter 9 Abstract Class & Interface Oum Saokosal , Head of IT Department National Polytechnic Institute of Cambodia Tel: (855)-12-417214 E-mail: oum_saokosal@yahoo.com

2. Interface

8. Why not use abstract class instead of interface? (1) Hey Rabbit! Today’s class is about interface. The word “interface” here means GUI, Graphical User Interface? Not at all, Ball. GUI is GUI. Interface here is a kind of ideas in OOP which is similar to abstract class. I’ll tell ya what...

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