Multimap implementation principle analysis in Java commonly used libraries

Multimap implementation principle analysis in Java commonly used libraries Introduction to Multimap Multimap is an interface in Java's commonly used library Collections. It is a data structure that can be mapped to multiple values.Unlike the traditional Map, Multimap allows a key to correspond to multiple values, providing more flexible data storage and operation methods.Multimap can easily handle complex data relationships such as one -to -one, more to more. 2. Multimap interface and implementation class The Multimap interface is part of the Java Collections Framework, which defines the basic operation of Multimap, including increasing, deleting, querying and iteration.The common implementation classes of the MULTIMAP interface have the following: 1. ArrayListMultimap: Use ArrayList storage value inside, which can allow repeated key values pairs. 2. Hashmultimap: Based on HashMap and HashSet, it is suitable for key values pairs that need to be heavy. 3. LinkedListMultimap: Use LinkedList storage value inside, suitable for key values that need to keep the insertion order. 4. TreeMultimap: Based on TreeMap and TreeSet, it is suitable for key value pairs that need to be sorted. 5. Setmultimap: The static method provided in the Multimaps class can generate instances of Setmultimap, which is suitable for different values per key. Third, the implementation principle of Multimap The implementation principle of Multimap mainly involves two key data structures: Map and Collection. 1. Map: In Multimap, MAP is used to store keys and values associated with it.Multimap's key is unique, each key is mapped to a collection of a value.The Multimap interface inherits from the Map interface, so it can operate Multimap like operating Map, such as Put, Get, Remove and other methods. 2. Collection: Multi -value parts in Multimap can store multiple values.Collection in Multimap is used to store multiple values. Different Multimap implementation classes use different collections to achieve storage values, such as ArrayList, LinkedList, HashSet, etc.Depending on the implementation class, the Collection may maintain the characteristics of insertion, sorting, or heavy weight. The implementation principle of MULTIMAP is based on the above MAP and Collection.The specific implementation process is as follows: 1. Use the mapping relationship between the MAP object storage key and value, where the key is unique. 2. Multi -values corresponding to each key with the Collection object. 3. For the PUT operation, store the mapping relationship of the key and values into the map, and add the value to the corresponding key's collection. 4. For the get operation, get the corresponding collection from the MAP and return the value in the collection. 5. For the Remove operation, first move the mapping relationship between the key and the value from the MAP, and then move the value from the corresponding key. Fourth, Multimap's application scenario Multimap is suitable for the following common application scenarios: 1. One -to -many mapping relationship: One key corresponds to multiple values, such as one class corresponds to multiple students, and one city corresponds to multiple attractions. 2. One -to -one mapping relationship: multiple keys correspond to the same value, such as multiple classes correspond to the same teacher, and multiple cities correspond to the same province. 3. Multiple -to -multiple mapping relationships: multiple keys correspond to multiple values. For example, one student chooses multiple courses and a user subscribes to multiple channels. The following is a sample code that demonstrates the use of Multimap: import com.google.common.collect.ArrayListMultimap; import com.google.common.collect.Multimap; public class MultimapExample { public static void main(String[] args) { // Create Multimap objects Multimap<String, String> multimap = ArrayListMultimap.create(); // Add key value pair multimap.put("key1", "value1"); multimap.put("key1", "value2"); multimap.put("key2", "value3"); multimap.put("key2", "value4"); // Get the value System.out.println("Values of key1: " + multimap.get("key1")); System.out.println("Values of key2: " + multimap.get("key2")); // iterate all key values pairs for (String key : multimap.keys()) { for (String value : multimap.get(key)) { System.out.println("Key: " + key + ", Value: " + value); } } } } This code uses ArrayListMultimap from the Google Guava library to demonstrate the basic use of Multimap.First create a Multimap object, and then use the PUT method to add a key value to the Multimap.Next, the corresponding value can be obtained through the key through the get method.Finally, you can iterate all the keys through the keys method and obtain the value of the corresponding key through the get method. Summarize: Multimap is an interface in Java's commonly used library Collections. The storage key can be mapped to multiple values.Its principle is based on the combination of MAP and Collection. It stores multiple values corresponding to each key through the mapping relationship between the MAP storage key and values.Multimap is suitable for one -to -many, more, one, and more mapping relationships, providing more flexible data storage and operation methods.