| Figure 10.1 shows the main interfaces of the Java Collections Framework, together with one otherIterablewhich is outside the Framework but is an essential adjunct to it. Its purpose is as follows: And the Framework interfaces have the following purposes: Collection contains the core functionality required of any collection other than a map. It has no direct concrete implementations; the concrete collection classes all implement one of its subinterfaces as well. Set is a collection, without duplicates, in which order is not significant. SortedSet automatically sorts its elements and returns them in order. NavigableSet extends this, adding methods to find the closest matches to a target element. Queue is a collection designed to accept elements at its tail for processing, yielding them up at its head in the order in which they are to be processed. Its subinterface Deque extends this by allowing elements to be added or removed at both head and tail. Queue and Deque have subinterfaces, BlockingQueue and BlockingDeque respectively, that support concurrent access and allow threads to be blocked, indefinitely or for a maximum time, until the requested operation can be carried out. List is a collection in which order is significant, accommodating duplicate elements. Map is a collection which uses key-value associations to store and retrieve elements. It is extended by ConcurrentMap, which provides support for concurrent access, by SortedMap, which guarantees to return its values in ascending key order, by NavigableMap which extends SortedMap to find the closest matches to a target element, and by ConcurrentNavigableMap which extends ConcurrentMap and NavigableMap.
Chapters 12 through 16 will concentrate on each of the Collections Framework interfaces in turn. First, though, in Chapter 11, we need to cover some preliminary ideas which run through the entire Framework design. Figure 10-1. The main interfaces of the Java Collections Framework 
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