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.
These two taken together implement about the simplest possible way to couple an event source with an event listener, without either of them having to know which type of class the other one is. So while they are being coupled, they're not closely coupled.
There is a good tutorial on developerWorks called "Java event delivery techniques" which demonstrates this and other event techniques. Observer/Observable are kind of obsolete through the advent of newer mechanism in later JDKs.