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Implementations
Set Implementations
List Implementations
Map Implementations
Queue Implementations
Deque Implementations
Wrapper Implementations
Convenience Implementations
Summary of Implementations
Questions and Exercises
Trail: Collections
Lesson: Implementations
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# 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.
- For the `Deque` interface, `ArrayDeque` 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 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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