Java How to Program (early objects), 9/e

20.11 Maps

Maps associate keys to values. The keys in a Map must be unique, but the associated values need not be. If a Map contains both unique keys and unique values, it’s said to implement a one-to-one mapping. If only the keys are unique, the Map is said to implement a many-to-one mapping —many keys can map to one value.

Maps differ from Setsinthat Maps contain keys and values, whereas Sets contain only values. Three of the several classes that implement interface Map are Hashtable, HashMap and TreeMap. Hashtablesand HashMaps store elements in hash tables, and TreeMaps store elements in trees. This section discusses hash tables and provides an example that uses a HashMap to store key/value pairs. Interface SortedMap extends Map and maintains ...