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copied!<p>Strings can cover a lot of use cases, but using more complicated objects can give you a lot more flexibility in your code. Seeing that in the US they've just announced the NCAA college basketball tournament seeds, I'll see if I can come up with a tournament-themed example.</p> <p>Suppose I want to build a Hashmap that stores all of the teams that are in each region. There are four regions to the tournament: East, West, Southwest, and Southeast. You could certainly create your map as:</p> <pre><code>HashMap<String, List<Team>> teamsInRegions = new HashMap<String, List<Team>>(); </code></pre> <p>But then, what if you already have an object that represents a region? You likely would, since each region has a lot more information associated with it than a name. For instance, I figure a Region class might look like:</p> <pre><code>public class Region { private String name; private Calendar firstRound; private String firstRoundLocation; private Calendar secondRound; private String secondRoundLocation; private Calendar thirdRound; private String thirdRoundLocation; .... } </code></pre> <p>You get the idea. If the HashMap were keyed by a String, you could certainly get away with having a reasonable Region.toString() method and using that as the key, but using the more complex object will allow you to write more flexible code.</p> <p>While others may disagree, I find myself using Maps in somewhat unpredictable ways sometimes, where calling HashMap.keySet() gives me a Set of fully populated, complex objects with a plethora of information. <strong>And</strong> having the Map there means I can use those objects to make decisions elsewhere as well.</p> <p>For instance, suppose I wanted to build up a list of all the locations of all the games in the basketball tournament. If I had my HashMap with complex objects, that would be as simple as:</p> <pre><code>Set<Region> regions = myMap.keyset(); Set<String> gameLocations = new HashSet(); for (Region region : regions) { gameLocations.add(region.getAllLocales()); } </code></pre> <p>And so on. YMMV.</p>

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