Java in a Nutshell, 5th Edition

Name

LinkedHashMap<K,V>

Synopsis

This class is a Map implementation based on a hashtable, just like its superclass HashMap. It defines no new public methods, and can be used exactly as HashMap is used. What is unique about this Map is that in addition to the hashtable data structure, it also uses a doubly-linked list to connect the keys of the Map into an internal list which defines a predictable iteration order.

You can iterate through the keys or values of a LinkedHashMap by calling entrySet( ), keySet( ), or values( ) and then obtaining an Iterator for the returned collection, just as you would for a HashMap. When you do this, however, the keys and/or values are returned in a well-defined order rather than the essentially random order provided by a HashMap. The default ordering for LinkedHashMap is the insertion order of the key: the first key inserted into the Map is enumerated first (as is the value associated with it), and the last entry inserted is enumerated last. Note that this order is not affect by re-insertions. That is, if a LinkedHashMap contains a mapping from a key k to a value v1, and you call the put( ) method to map from k to a new value v2, this does not change the insertion order, or the iteration order of the key k. The iteration order of a value in the map is the iteration order of the key with which it is associated.

Insertion order is the default iteration order for this class, but if you instantiate a LinkedHashMap with the three-argument constructor, and pass ...