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.
Immutable means that, once an object is instatiated, it can't be changed. I'd say that the wrapper classes and String are better examples than Math. Math can't be instatiated at all so there isn't much sense in saying that it's immutable. Just because a class is final, it isn't necessarily immutable, and vice-versa. Corey