Set,
List
,
or Map
.
It was compiled for Java 1.4. Many additions
have been made to the Collections Framework since then (notably the
Queue
and
Deque
interfaces, and various items in java.util.concurrent
).
These later additions have been omitted here, since this briefer summary should suffice for most cases.
The best general purpose or 'primary' implementations are likely ArrayList
, LinkedHashMap
, and
LinkedHashSet
. Their overall performance is better, and you should use them
unless you need a special feature provided by another implementation. That
special feature is usually ordering or sorting.
For convenience, "ordering" will here refer to the order of items returned by an Iterator
,
and "sorting" will here refer to sorting items according to Comparable
or Comparator
.
Interface | HasDuplicates? | Implementations | Historical | ||||
Set |
no | HashSet |
... | LinkedHashSet |
... | TreeSet |
|
List |
yes | ... | ArrayList |
... | LinkedList |
|
Vector,
Stack |
Map |
no duplicate keys | HashMap |
... | LinkedHashMap |
... | TreeMap |
Hashtable,
Properties |
Principal features of non-primary implementations:
HashMap
has slightly better performance than LinkedHashMap
, but its iteration order is
undefined
HashSet
has slightly better performance than LinkedHashSet
, but its iteration
order is undefined TreeSet
is ordered and sorted, but slowerTreeMap
is ordered and sorted, but slowerLinkedList
has fast adding to the start of the list, and fast
deletion from the interior via iterationHashSet
- undefinedHashMap
- undefinedLinkedHashSet
- insertion orderLinkedHashMap
- insertion order of keys (by default), or 'access order'ArrayList
- insertion orderLinkedList
- insertion orderTreeSet
- ascending order, according to Comparable
/ Comparator
TreeMap
- ascending order of keys, according to Comparable
/ Comparator
LinkedHashSet
and LinkedHashMap
, the re-insertion
of an item does not affect insertion order.
For LinkedHashMap
, 'access order' is from the least recent access
to the most recent access. In this context, only calls to get
,
put
,
and putAll
constitute an access, and only calls to these methods
affect access order.
While being used in a Map
or Set
, these items must
not change state (hence, it's recommended that these items be immutable
objects):
Map
Set
Comparable
Comparator
for the stored objects be definedResultSet
as specified in an ORDER BY
clause, insert the records into a List
or a LinkedHashMap
.