java 如何使用多组映射。 jar：http：//mvnrepository.com/artifact/com.google.guava/guava/14.0

Posted 2021-05-08

<dependency>
    <groupId>com.google.guava</groupId>
    <artifactId>guava</artifactId>
    <version>14.0</version>
</dependency>

public class MutliMapTest {
    public static void main(String... args) {
        Multimap<String, String> myMultimap = ArrayListMultimap.create();

        // Adding some key/value
        myMultimap.put("Fruits", "Banana");
        myMultimap.put("Fruits", "Apple");
        myMultimap.put("Fruits", "Pear");
        myMultimap.put("Vegetables", "Carrot");

        // Getting the size
        int size = myMultimap.size();
        System.out.println(size); // 4

        // Getting values
        Collection<String> fruits = myMultimap.get("Fruits")
        System.out.println(fruits); // [Banana, Apple, Pear]
        Collection<String> vegetables = myMultimap.get("Vegetables");
        System.out.println(vegetables); // [Carrot]

        // Iterating over entire Mutlimap
        for(String value : myMultimap.values()) {
            System.out.println(value);
        }

        // Removing a single value
        myMultimap.remove("Fruits","Pear");
        System.out.println(myMultimap.get("Fruits")); // [Banana, Apple]

        // Remove all values for a key
        myMultimap.removeAll("Fruits");
        System.out.println(myMultimap.get("Fruits")); // [] (Empty Collection!)
        
        List<String> myValues = myMutlimap.get("myKey"); // Returns a List, not a Collection
    }
}