Detailed explanation of the Multimap framework in Java commonly used libraries
Detailed explanation of the Multimap framework in Java commonly used libraries
In Java, Multimap is a very useful data structure that allows mapping one key to multiple values.In Java's Collections library, we can use the Multimap interface and its implementation class to achieve the storage and operation of this key value pair.This article will introduce the concepts, usage, and several common implementation classes of the Multimap framework in detail.
What is Multimap?
Multimap is a collection of a key value pair, and one key can be mapped to multiple values.The traditional MAP interface allows only one key to map to one value, and Multimap relaxes this limit, which can associate multiple values on one key.
Multimap interface
In Java's Collections library, the Multimap interface defines the main method of the Multimap framework.It is a generic interface that defines the following important methods:
-Put (key, value): Add the specified key value pair to Multimap.
-GET (key): Return all the sets of all values associated with the specified key.
-Rmove (key, value): Remove the specified key value pair from Multimap.
-KeySet (): Return to the set of all keys in Multimap.
-VALUES (): Return to all the sets of all values in Multimap.
-Entries (): Return to the set of all key values pairs in Multimap.
-Size (): Return the total number of key pairs in Multimap.
Multimap interface implementation class
In Java's Collections library, there are several implementation classes in the Multimap interface, which are:
-ArrayListMultimap: Multimap based on ArrayList can store multiple values under the same key.
-LinkedListMultimap: Multimap based on LinkedList can also store multiple values under the same key.
-Hashmultimap: Multimap based on HashMap and Hashset can store multiple values under the same key, and the order of value is uncertain.
-Linkedhashmultimap: Multimap based on Linkedhashmap and Linkedhashset can maintain the order of key value pairs.
-Treemultimap: Multimap based on TreeMap and TreeSet, the key and values are sorted in the natural order.
-IMMUTableMultimap: Unable to be changed after creation cannot be modified.
Below is a simple example of using ArrayListMultimap:
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]
System.out.println (multimap.get ("key2"); // output [2]
multimap.remove("key1", 1);
System.out.println (multimap.get ("key1"); // output [3]
System.out.println (multimap.size ()); // Output 2
}
}
In the above example, we first created an ArrayListMultimap instance, and used the PUT method to add a few key values to the Multimap.Then use the get method to get all the value corresponding to the specified key.Then use the Remove method to remove a key value pair.Finally, the total number of key values pairs in Multimap output the total value pair of key values in Multimap output.
in conclusion
Multimap is a very useful data structure in Java's Collections library that allows one key to multiple values.Through the Multimap framework, we can more conveniently operate the key values of the collection to improve the flexibility and readability of the code.In actual development, choosing the appropriate Multimap implementation class according to needs can greatly simplify our programming work.
