Guava Multimap – HashMultimap Implementation Example – Developers Corner

Guava Multimap – HashMultimap Implementation

The HashMultimap is a variation of a Map in which multiple values or objects are associated with a single key but it does not allow duplicate key/value pairs in the Map. In this example, you will notice that the value of Amaury Valdes appears only once in the Multimap element with a key of 777. Notice how duplicates are not allowed and silently fail to be added.

Methods available to HashMultimap

@GwtCompatible
public interface Multimap<K,V>

#	Method and Description
1	Map<K,Collection<V>> asMap() Returns a view of this multimap as a Map from each distinct key to the nonempty collection of that key’s associated values.
2	void clear() Removes all key-value pairs from the multimap, leaving it empty.
3	boolean containsEntry(Object key, Object value) Returns true if this multimap contains at least one key-value pair with the key key and the value value.
4	boolean containsKey(Object keyName) Returns true if this multimap contains at least one key-value pair with the key keyName.
5	boolean containsValue(Object valueName) Returns true if this multimap contains at least one key-value pair with the value valueName.
6	static <K,V> HashMultimap<K,V> create() Creates a new, empty HashMultimap with the default initial capacities.
7	static <K,V> HashMultimap<K,V> create(int expectedKeys, int expectedValuesPerKey) Constructs an empty HashMultimap with enough capacity to hold the specified numbers of keys and values without rehashing.
8	static <K,V> HashMultimap<K,V> create(Multimap<? extends K,? extends V> multimap) Constructs a HashMultimap with the same mappings as the specified multimap.
9	Set<Map.Entry<K,V>> entries() Returns a view collection of all key-value pairs contained in this multimap, as Map.Entry instances.
10	boolean equals(Object obj) Compares the specified object with this multimap for equality.
11	Set<V> get(K key) Returns a view collection of the values associated with key in this multimap, if any.
12	int hashCode() Returns the hash code for this multimap.
13	boolean isEmpty() Returns true if this multimap contains no key-value pairs.
14	Multiset<K> keys() Returns a view collection containing the key from each key-value pair in this multimap, without collapsing duplicates.
15	Set<K> keySet() Returns a view collection of all distinct keys contained in this multimap.
16	boolean put(K key, V value) Stores a key-value pair in this multimap.
17	boolean putAll(K key, Iterable<? extends V> values) Stores a key-value pair in this multimap for each of values, all using the same key, key.
18	boolean putAll(Multimap<? extends K,? extends V> multimap) Stores all key-value pairs of multimap in this multimap, in the order returned by multimap.entries().
19	boolean remove(Object key, Object value) Removes a single key-value pair with the key key and the value value from this multimap, if such exists.
20	Set<V> removeAll(Object keyName) Removes all values associated with the key keyName.
21	Set<V> replaceValues(K key, Iterable<? extends V> values) Stores a collection of values with the same key, replacing any existing values for that key.
22	int size() Returns the number of key-value pairs in this multimap.
23	Collection<V> values() Returns a view collection containing the value from each key-value pair contained in this multimap, without collapsing duplicates (so values().size() == size()).

Java HashMultimap Example of Guava Multimap

package com.avaldes;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.google.common.collect.ArrayListMultimap;
import com.google.common.collect.HashMultimap;
import com.google.common.collect.Multimap;
import com.google.common.collect.SortedSetMultimap;
import com.google.common.collect.TreeMultimap;

public class GuavaSetMultiMapExample {
  
  public static void main(String[] args) {
    Logger logger = LoggerFactory.getLogger(GuavaSetMultiMapExample.class);

    logger.info("---myHashMultimap----------");
    logger.info("No duplicates allowed, Not Sorted...");
    Multimap<String,String> myHashMultimap = HashMultimap.create();
    myHashMultimap.put("777", "Amaury Valdes");
    myHashMultimap.put("777", "Walter White");
    myHashMultimap.put("777", "John Smith");
    myHashMultimap.put("777", "Eric Hamlin");
    myHashMultimap.put("777", "Amaury Valdes");
    
    logger.info("myHashMultimap: " + myHashMultimap);
  }
}

Output

22:02:55.609 [main] INFO  com.avaldes.GuavaSetMultiMapExample - ---myHashMultimap----------
22:02:55.614 [main] INFO  com.avaldes.GuavaSetMultiMapExample - No duplicates allowed, Not Sorted...
22:02:55.635 [main] INFO  com.avaldes.GuavaSetMultiMapExample - myHashMultimap: {777=[Amaury Valdes, Walter White, John Smith, Eric Hamlin]}

That’s It!

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GuavaHashMultimap

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