Summary of Implementations

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Trail: Collections
Lesson: Implementations

## Summary of Implementations

> 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:

> - 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.
> Each of the general-purpose implementations provides all optional operations contained in its interface.

> 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 are thread-safe but not governed by a single exclusion lock.

> The `Collections` class (as opposed to the `Collection` 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.

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