Implementations are the data objects used to store collections, which implement the interfaces described in the Interfaces lesson .The Java Collections Framework provides several general-purpose implementations of the core interfaces:
Each of the general-purpose implementations provides all optional operations contained in its interface.
- For the
Set
interface,HashSet
is the most commonly used implementation.- For the
List
interface,ArrayList
is the most commonly used implementation.- For the
Map
interface,HashMap
is the most commonly used implementation.- For the
Queue
interface,LinkedList
is the most commonly used implementation.The Java Collections Framework also provides several special-purpose implementations for situations that require nonstandard performance, usage restrictions, or other unusual behavior.
The
java.util.concurrent
package contains several collections implementations, which are thread-safe but not governed by a single exclusion lock.The
Collections
class (as opposed to theCollection
interface), provides static methods that operate on or return collections, which are known as Wrapper implementations.Finally, there are several Convenience implementations, which can be more efficient than general-purpose implementations when you don't need their full power. The Convenience implementations are made available through static factory methods.