CODEWITHSUNDEEP
javadata-structures
Zombies
Zombies

Reputation: 25872

Java Map that is Multi Value and supports generics?

I noticed that there is a MultiValueMap from commons, however it doesn't support generics. Is there such a map that does?

Upvotes: 7

Views: 3779

Answers (4)

gavenkoa
gavenkoa

Reputation: 48753

https://mvnrepository.com/artifact/org.apache.commons/commons-collections4 since Nov, 2013 supports generic collections! No need to bring Guava to the table.

Just import classes from org.apache.commons.collections4 instead of org.apache.commons.collections:

import org.apache.commons.collections4.MultiValuedMap;
import org.apache.commons.collections4.multimap.ArrayListValuedHashMap;

private MultiValuedMap<String, Employee> nameLookup = new ArrayListValuedHashMap<>();

http://commons.apache.org/proper/commons-collections/apidocs/org/apache/commons/collections4/MultiMap.html

Upvotes: 0

Tomasz Nurkiewicz
Tomasz Nurkiewicz

Reputation: 340723

Probably Guava is a better choice but if you really want to stick with Commons collections API:

http://sourceforge.net/projects/collections

A Java 5 generics-enabled version of the popular Jakarta Commons-Collections project. All appropriate classes from Commons-Collections 3.1 have been refactored to support Java generics.

Upvotes: 2

Matt Ball
Matt Ball

Reputation: 359786

Absolutely! Check out Google Guava's Multimaps.

Multimap<Foo, Bar> mm = new ListMultimap<Foo, Bar>();
// fill it however...
Foo foo = ...;
Collection<Bar> bars = mm.get(foo);

Upvotes: 5

Peter Lawrey
Peter Lawrey

Reputation: 533492

Have you tried Guava's Multimap?

A collection similar to a Map, but which may associate multiple values with a single key. If you call put(K, V) twice, with the same key but different values, the multimap contains mappings from the key to both values.

Depending on the implementation, a multimap may or may not allow duplicate key-value pairs. In other words, the multimap contents after adding the same key and value twice varies between implementations. In multimaps allowing duplicates, the multimap will contain two mappings, and get will return a collection that includes the value twice. In multimaps not supporting duplicates, the multimap will contain a single mapping from the key to the value, and get will return a collection that includes the value once.

http://guava-libraries.googlecode.com/svn/trunk/javadoc/com/google/common/collect/Multimap.html

Upvotes: 11

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