<dependency> <groupId>com.google.guava</groupId> <artifactId>guava</artifactId> <version>30.1-jre</version> </dependency> 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("key1", 2); multimap.put("key2", 3); multimap.put("key2", 4); } }