What collection types are there in java?

#There are three main collection types in Java: set (set), list (list) and map (mapping).

1, List (orderly, duplicate) (Recommended learning: java course )

List Ordered and repeatable, List focuses on indexes and has a series of methods related to indexes, making query speed fast. Because when inserting or deleting data into the list collection, it will be accompanied by the movement of subsequent data, all insertion and deletion of data are slow.

2. Set (unordered, cannot be repeated)

The objects stored in Set are unordered and cannot be repeated. The objects in the set are not in a specific way. Sorting simply adds objects to a collection.

3. Map (key-value pairs, unique keys, non-unique values)

The Map collection stores key-value pairs. Keys cannot be repeated, but values ​​can be repeated. . Obtain the value according to the key. When traversing the map collection, first obtain the set collection of the key, traverse the set collection, and obtain the corresponding value.

The collection class has three characteristics:

First, the collection class framework is high-performance. The implementation of the basic set of classes (dynamic arrays, linked lists, trees, and hash tables) is efficient. Most people rarely change these already mature and efficient APIs;

Second point, the collection class allows different types of collections to work in the same way and with a high degree of interoperability;

Third point Points are that the collection class is easy to extend and modify, and programmers can easily modify it to meet their own data structure needs.

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