Multimap framework introduction and use in the Java class library

Multimap framework introduction and use in the Java class library In Java development, we often need to process the collection of key values pairs. One of the common requirements is the condition that the key corresponds to multiple values.The Multimap framework in the Java class library is designed to solve this situation.MULTIMAP can be understood as "a mapping of multiple values", which provides a convenient data structure to handle a pair of relationships. The Multimap framework is an important component in the Google Guava library, which is very practical in the scene of processing multiple values.By using Multimap, we do not need to manually create and manage the set of values corresponding to each key. Instead, we can directly add the value to the corresponding set of the key to simplify the writing and maintenance of the code. The use of the Multimap framework can greatly simplify our data operation, and also improve the readability and maintenance of the code.Below we will introduce the use of Multimap and provide some example code. First of all, we need to introduce the dependencies of the GUAVA library in the project, as shown below: <dependency> <groupId>com.google.guava</groupId> <artifactId>guava</artifactId> <version>XXXX</version> </dependency> Next, we can start using the Multimap framework. 1. Create Multimap object We can use the implementation class of the Multimap interface to create Multimap objects.The Guava library provides two commonly used implementation classes: ArrayListMultimap and Hashmultimap. Multimap<String, Integer> multimap = ArrayListMultimap.create(); The above code creates a Multimap object with a string as a key and an integer value. 2. Add key value pair Use the PUT () method to add key values to the Multimap object.If the key already exists, add the value to the corresponding set. multimap.put("key1", 1); multimap.put("key1", 2); multimap.put("key2", 3); The above code is added to the value set of 1 and 2 to the corresponding value set of KEY1, and 3 is added to the value set corresponding to the key2. 3. Get all the value corresponding to the key Use the get () method to get all the value corresponding to the key. Collection<Integer> values = multimap.get("key1"); The above code will return a set containing all values corresponding to Key1. 4. Get all the keys of Multimap Use the keyset () method to get all the keys of the Multimap object. Set<String> keys = multimap.keySet(); The above code will return a collection of all keys containing Multimap objects. 5. Get all the value of Multimap Use the Values () method to obtain all the values of the Multimap object. Collection<Integer> allValues = multimap.values(); The above code will return a collection of all values containing the Multimap object. 6. Use the iterator to traverse Multimap Entries () methods of Multimap objects can return a collection of all key values pairs in Multimap. for (Map.Entry<String, Integer> entry : multimap.entries()) { String key = entry.getKey(); Integer value = entry.getValue(); System.out.println("key: " + key + ", value: " + value); } The above code will traverse all the key values in Multimap and print it out. The Multimap framework provides us with convenience and flexibility for dealing with a pair of relationships.Multimap is a very useful tool whether it is processing configuration files, log data or other similar cases.By using the Multimap framework reasonably, we can improve the readability and maintenance of the code, thereby developing Java applications more efficiently. This is the introduction and use of the Multimap framework in the Java class library.I hope this article will help you!