This week's book giveaway is in the General Computing forum. We're giving away four copies of Arduino in Action and have Martin Evans, Joshua Noble, and Jordan Hochenbaum on-line! See this thread for details.
Implementing the Comparable interface enables you to define one way to compare instances of your class. However, objects are sometimes comparable in many ways. For example, two Person objects may need to be compared by age or by last/first name. In cases like this, create a Comparator that defines how to compare two objects. To make objects comparable in two ways, then you need two comparators.