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copied!<p>Essentially type safety and convenience.</p> <p>Java implements its generics by a mechanism known as type erasure which effectively replaces the generic definition with a non-generic definition at compile time. The reason this was done was to maintain API compatability between 1.4 and 1.5 - the collections API may well have been updated but if you accessed it in a non-generic way in 1.5 it would work the same.</p> <p>The difference was that if you intended a collection to only contain particular types of objects you could explictly encode that requirement in your APIs and avoid issues such as receiving a list with the wrong type of objects in it - and also the need to have to explictly cast those objects making your code simpler to read and less error prone.</p> <p>You would use the generics for essentially the same reasons as when they are used with collections - when you need to say that an object is a composite of other objects, but that there may be a range of types possible for that composition and that once bound the addition of these new objects implies a new composite type disimilar to other similar composites. That is to say a list of strings is similar in type to a list of integers but they are no longer compatible with each other.</p> <p>One example of this is in the <code>Future</code> where you are waiting for an asynchronous result. The <code>Future</code> class encapsulates the concept of the asynchronous result, but the specific type of <code>Future</code> such as <code>Future<String></code> futher specifies what type of result you can expect - and makes it distinct from <code>Future<Integer></code>.</p>

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