This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
Alan is right: An enum is like a special kind of class, and an instance of it is made for each enum constant. Since you have two constants, BIG and SMALL, two instances are made. Note that Java enums are very flexible. You can, for example, add member variables and methods to an enum. See this for some examples: Java Enums.