Map Classes
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title: Map Implementation Classes - Hashtable, LinkedHashMap, and TreeMap
Hashtable is a legacy class that differs from HashMap in two ways:
* Hashtable does not allow null keys.
* Hashtable's methods are synchronized (thread-safe, slower), while HashMap's are not.
Maintaining Key Order¶
Two other implementation classes will maintain an ordering of the keys.
LinkedHashMap adds ordered iteration to HashMap.
* The keySet() method will return a Set of keys that are in insertion order.
TreeMap implements the SortedMap interface.
* TreeMap objects are sorted based upon the key at the time of insertion and removal.
* keySet() returns a Set of keys in ascending order.
Drill¶
MapInterface/com.example.mapinterface.drills.AreaCodeDrillThis drill has you use different types of
Maps to see how keys are ordered. * Follow instructions in the class, in numeric order. 1. Add key-value pairs 2. Finish theoutputMapDatamethod 3. Use aTreeMapingenerateMapData4. Use aLinkedHashMapingenerateMapData