The difference and connection between the Multimap framework of the Multimap framework in the Java class library

The difference and connection between the Multimap framework and Map introduction: In the Java class library Collections, the Multimap framework provides a more flexible data structure than a standard MAP interface.Although Multimap and Map have some of them in common, they also have some important differences.In this article, we will explore the differences and connections between the Multimap framework and Map, and provide some Java code examples to help readers better understand the difference between the two. the difference: 1. Storage structure: -Map: Map is a collection of key value pairs, where each key is unique.The corresponding value can be retrieved through the key. -Multimap: Multimap is also a collection of key value pairs, but each key can correspond to multiple values.This means that in Multimap, a key can be mapped to multiple values. 2. Repeat the key: -Map: Map is not allowed to repeat the key.If you use the same key to add a new value, the old value will be covered. -Multimap: Multimap is allowed to repeat the key.The same key can be mapped to different values multiple times. 3. Type constraint: -Map: In Map, a key can only be mapped to one value.Therefore, the value of MAP is a single data type.For example, a map may be `Map <string, Integer>`, where the key is a string and an integer. -Multimap: One key in Multimap can be mapped to multiple values.This means that Multimap can contain different types of values.For example, a Multimap may be `Multimap <string, Object>`, where the key is a string, and the value can be any object. 4. Data structure: -Map: Map has multiple implementation classes, including HashMap, Linkedhashmap, TreeMap, etc.These implementation classes are different in terms of performance and sequentiality, but they all find values through keys. -Multimap: Multimap also has multiple implementation classes, including ArrayListMultimap, LinkedListMultimap and Hashmultimap.These implementation classes allow the key to mappore multiple values and provide a convenient method to add and retrieve these values. connect: Although Multimap is different from MAP in some aspects, there are some connections between them: -Multimap is an extension of MAP. You can use many methods and operations similar to MAP using Multimap. -Multimap inherits some common methods in the Map interface, such as `size ()`, `isempty (), and` containskey () `, etc. -In use Multimap, it can be regarded as a mapping relationship between the key to the value set, and these values can be a data structure of the list, collection or other types of types. Example code: Below is a simple sample code using the Multimap framework: import com.google.common.collect.ArrayListMultimap; import com.google.common.collect.Multimap; public class MultimapExample { public static void main(String[] args) { Multimap<String, Integer> multimap = ArrayListMultimap.create(); multimap.put("key1", 1); multimap.put("key2", 2); multimap.put("key1", 3); System.out.println (multimap.get ("key1"); // Output: [1, 3] } } In the above sample code, we use the Multimap implementation of the Multimap in the Google Guava library to implement the ArrayListMultimap.We use the `put ()` method to add key value pairs to Multimap, and then retrieve all values of the corresponding key through the `Get ()" method.In Multimap, a key can be mapped to multiple values, so the output is `[1, 3]`. in conclusion: The Multimap framework and MAP are different in terms of storage structure, keys, type constraints, and data structures.Despite the difference, Multimap is still an extension of the Map, which provides a more flexible data structure that can mappore multiple values to one key.By understanding the differences and connections between Multimap and Map, developers can choose suitable data structures according to their needs to store and operate data.