> The initial APIs of this module are supported since API version 8. Newly added APIs will be marked with a superscript to indicate their earliest API version.
**ArrayList** is a linear data structure that is implemented based on arrays. **ArrayList** can dynamically adjust the capacity based on project requirements. It increases the capacity by 50% each time.
Similar to **ArrayList**, **[Vector](js-apis-vector.md)** is also implemented based on arrays and can dynamically adjust the capacity. It increases the capability by 100% each time.
When compared with **[LinkedList](js-apis-linkedlist.md)**, **ArrayList** is more efficient in random access but less efficient in the addition or removal operation, because its addition or removal operation affects the position of other elements in the container.
**Recommended use case**: Use **ArrayList** when elements in a container need to be frequently read.
Obtains entries within a range in this container, including the entry at the start position but not that at the end position, and returns these entries as a new **ArrayList** instance.
Obtains elements within a range in this container, including the element at the start position but not that at the end position, and returns these elements as a new **ArrayList** instance.
> The initial APIs of this module are supported since API version 8. Newly added APIs will be marked with a superscript to indicate their earliest API version.
Double-ended queue (deque) is a sequence container implemented based on the queue data structure that follows the principles of First In First Out (FIFO) and Last In First Out (LIFO). It allows insertion and removal of elements at both the ends. **Deque** can dynamically adjust the capacity based on project requirements. It doubles the capacity each time. **Deque** differs from **[Queue](js-apis-queue.md)** and **[Vector](js-apis-vector.md)** mainly in the following aspects:
**Queue** follows the principle of FIFO only and allows element removal at the front and insertion at the rear.
**Vector** supports insertion and deletion of elements in between, as well asat both the ends. When compared with **Vector**, **Deque** is more efficient in inserting and removing header elements, but less efficient in accessing elements.
**Recommended use case**: Use **Deque** when you need to frequently insert or remove elements at both the ends of a container.
> The initial APIs of this module are supported since API version 8. Newly added APIs will be marked with a superscript to indicate their earliest API version.
**HashMap** is a map implemented based on the array, linked list, and red-black tree. It provides efficient data query, insertion, and removal. The elements in a **HashMap** instance are mappings of key-value pairs. Each key must be unique and have only one value.
**HashMap** is faster in accessing data than **[TreeMap](js-apis-treemap.md)**, because the former accesses the keys based on the hash codes, whereas the latter stores and accesses the keys in sorted order.
**[HashSet](js-apis-hashset.md)** is implemented based on **HashMap**. The input parameter of **HashMap** consists of **key** and **value**. In **HashSet**, only the **value** object is processed.
**Recommended use case**: Use **HashMap** when you need to quickly access, remove, and insert key-value pairs.
> The initial APIs of this module are supported since API version 8. Newly added APIs will be marked with a superscript to indicate their earliest API version.
**HashSet** is implemented based on [HashMap](js-apis-hashmap.md). In **HashSet**, only the **value** object is processed.
Unlike [TreeSet](js-apis-treeset.md), which stores and accesses data in sorted order, **HashSet** stores data in a random order. This means that **HashSet** may use a different order when storing and accessing elements. Both of them allows only unique elements. However, null values are allowed in **HashSet**, but not allowed in **TreeSet**.
**Recommended use case**: Use **HashSet** when you need a set that has only unique elements or need to deduplicate a set.
> The initial APIs of this module are supported since API version 8. Newly added APIs will be marked with a superscript to indicate their earliest API version.
**LightWeightMap** stores key-value (KV) pairs. Each key must be unique and have only one value.
**LightWeightMap** is based on generics and uses a lightweight structure. Keys in the map are searched using hash values, which are stored in an array.
Compared with **[HashMap](js-apis-hashmap.md)**, which can also store KV pairs, **LightWeightMap** occupies less memory.
**Recommended use case**: Use LightWeightMap when you need to store and access **KV pairs**.
> The initial APIs of this module are supported since API version 8. Newly added APIs will be marked with a superscript to indicate their earliest API version.
**LightWeightSet** stores a set of values, each of which must be unique.
**LightWeightSet** is based on generics and uses a lightweight structure. Its default initial capacity is 8, and it has the capacity doubled in each expansion.
The values in such a set are searched using hash values, which are stored in an array.
Compared with **[HashSet](js-apis-hashset.md)**, which can also store values, **LightWeightSet** occupies less memory.
**Recommended use case**: Use **LightWeightSet** when you need a set that has only unique elements or need to deduplicate a set.
> The initial APIs of this module are supported since API version 8. Newly added APIs will be marked with a superscript to indicate their earliest API version.
**LinkedList** is implemented based on the doubly linked list. Each node of the doubly linked list has references pointing to the previous element and the next element. When querying an element, the system traverses the list from the beginning or end. **LinkedList** offers efficient insertion and removal operations but supports low query efficiency. **LinkedList** allows null elements.
Unlike **[List](js-apis-list.md)**, which is a singly linked list, **LinkedList** is a doubly linked list that supports insertion and removal at both ends.
**LinkedList** is less efficient in data access than **[ArrayList](js-apis-arraylist.md)**.
**Recommended use case**: Use **LinkedList** for frequent insertion and removal operations.
> The initial APIs of this module are supported since API version 8. Newly added APIs will be marked with a superscript to indicate their earliest API version.
**List** is implemented based on the singly linked list. Each node has a reference pointing to the next element. When querying an element, the system traverses the list from the beginning. **List** offers efficient insertion and removal operations but supports low query efficiency. **List** allows null elements.
Unlike [LinkedList](js-apis-linkedlist.md), which is a doubly linked list, **List** is a singly linked list that does not support insertion or removal at both ends.
**Recommended use case**: Use **List** for frequent insertion and removal operations.
Obtains entries within a range in this container, including the entry at the start position but not that at the end position, and returns these entries as a new **List** instance.
Obtains elements within a range in this container, including the element at the start position but not that at the end position, and returns these elements as a new **List** instance.
> The initial APIs of this module are supported since API version 8. Newly added APIs will be marked with a superscript to indicate their earliest API version.
**PlainArray** stores key-value (KV) pairs. Each key must be unique, be of the number type, and have only one value.
**PlainArray** is based on generics and uses a lightweight structure. Keys in the array are searched using binary search, which map to values in other arrays.
Both **PlainArray** and **[LightWeightMap](js-apis-lightweightmap.md)** are used to store KV pairs in the lightweight structure. However, the key type of **PlainArray** can only be **number**.
**Recommended use case**: Use **PlainArray** when you need to store KV pairs whose keys are of the **number** type.
> The initial APIs of this module are supported since API version 8. Newly added APIs will be marked with a superscript to indicate their earliest API version.
**Queue** follows the principle of First In First Out (FIFO). It supports insertion of elements at the end and removal from the front of the queue. **Queue** is implemented based on the queue data structure.
Unlike **[Deque](js-apis-deque.md)**, which supports insertion and removal at both the ends, **Queue** supports insertion at one end and removal at the other end.
**Recommended use case**: Use **Queue** in FIFO scenarios.
> The initial APIs of this module are supported since API version 8. Newly added APIs will be marked with a superscript to indicate their earliest API version.
**Stack** is implemented based on the array data structure. It follows the principle Last Out First In (LOFI) and supports data insertion and removal at one end.
Unlike **[Queue](js-apis-queue.md)**, which is implemented based on the queue data structure and supports insertion at one end and removal at the other end, **Stack** supports insertion and removal at the same end.
**Recommended use case**: Use **Stack** in LOFI scenarios.
> The initial APIs of this module are supported since API version 8. Newly added APIs will be marked with a superscript to indicate their earliest API version.
**TreeMap** stores key-value (KV) pairs. Each key must be unique and have only one value.
**TreeMap** is implemented using a red-black tree, which is a binary search tree where keys are stored in sorted order for efficient insertion and removal.
**[HashMap](js-apis-treemap.md)** is faster in accessing data than **TreeMap**, because the former accesses data based on the hash code of the key, whereas the latter stores and accesses the keys in sorted order.
Recommended use case: Use **TreeMap** when you need to store KV pairs in sorted order.
> The initial APIs of this module are supported since API version 8. Newly added APIs will be marked with a superscript to indicate their earliest API version.
**TreeSet** is implemented based on **[TreeMap](js-apis-treemap.md)**. In **TreeSet**, only **value** objects are processed. **TreeSet** can be used to store values, each of which must be unique.
**[HashSet](js-apis-hashset.md)** stores data in a random order, whereas **TreeSet** stores data in sorted order. Both of them allows only unique elements. However, null values are allowed in **HashSet**, but not allowed in **TreeSet**.
Recommended use case: Use **TreeSet** when you need to store data in sorted order.
