<dependencies> <dependency> <groupId>org.apache.commons</groupId> <artifactId>commons-collections4</artifactId> <version>4.4</version> </dependency> </dependencies> import org.apache.commons.collections4.CollectionUtils; List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5); import org.apache.commons.collections4.CollectionUtils; import org.apache.commons.collections4.collection.SynchronizedCollection; Collection<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5); import org.apache.commons.collections4.Bag; import org.apache.commons.collections4.bag.HashBag; Bag<String> bag = new HashBag<>();