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.
the Date class implements Comparable, so it is also possible to use the compareTo method. eg
Sven's probosal with the getTime() is more precise as you can obtain the exact milliseconds between the Date objects. Anyway, when you want to determine days, hours and so on between the dates, you should get an instance of the Calendar class (also in java.util) and work with this.