Once you get the jar added to your project, you can start cruising the
javadoc and seeing what you can make of the Apache collections classes (and interfaces, mind you).
This will take you a few steps beyond the humble plateau of plain-vanilla Maps and Lists, by introducing variations of Sets and different types of Maps, designed for special scenarios. But before you ascend to the Java data structure stratosphere, you might want to recap your knowledge on the basic interfaces in the Collections framework, such as the
Map interface, and the
List interface. An interesting point of comparison, is that while the Map interface has no superinterfaces, the List interface is superinterface'd by the
Collection interface and the
Iterable interface by extension, since Collections are by necessity Iterable.
Perhaps, you are interested in the numerous implementations of Bags (sets that allow repeat elements e.g. two pairs of socks in a gym bag), and wander over to
TreeBag or
HashBag (now deprecated). Also fascinating are the various implementations of the
BidiMap interface such as
TreeBidiMap, that allows lookup from keys to values and values to keys- with equal efficiency. It is more storage efficient than using two separate TreeMaps, although the
DualTreeBidiMap does use this approach.
Remember always the distinction between interfaces and classes, do not try to create an object of type Bag by instantiating Bag, but rather create an instance of TreeBag (but not HashBag) i.e. instantiate the implementing classes (but not deprecated ones!)
