A Bag/ultiset stores each object in the collection together with a count of occurrences. Extra methods on the interface allow multiple copies of an object to be added or removed at once. JDK analog is HashMap<T, Integer>, when values is count of copies this key.

Type	Guava	Apache Commons Collections	GS Collections	JDK
Order not defined	HashMultiset	HashBag	HashBag	HashMap
Sorted	TreeMultiset	TreeBag	TreeBag	TreeMap
Insertion-order	LinkedHashMultiset	-	-	LinkedHashMap
Concurrent variant	ConcurrentHashMultiset	SynchronizedBag	SynchronizedBag	Collections.synchronizedMap(HashMap<String, Integer>)
Concurrent and sorted	-	SynchronizedSortedBag	SynchronizedSortedBag	Collections.synchronizedSortedMap(TreeMap<String,Integer>)
Immutable collection	ImmutableMultiset	UnmodifiableBag	UnmodifiableBag	Collections.unmodifiableMap(HashMap<String, Integer)]
Immutable and sorted	ImmutableSortedMultiset	UnmodifiableSortedBag	UnmodifiableSortedBag	Collections.unmodifiableSortedMap(TreeMap<String, Integer>)

Examples:

1. Using SynchronizedSortedBag from Apache:

    // Parse text to separate words
    String INPUT_TEXT = "Hello World! Hello All! Hi World!";
    // Create Multiset
    Bag bag = SynchronizedSortedBag.synchronizedBag(new TreeBag(Arrays.asList(INPUT_TEXT.split(" "))));

    // Print count words
    System.out.println(bag); // print [1:All!,2:Hello,1:Hi,2:World!]- in natural (alphabet) order
    // Print all unique words
    System.out.println(bag.uniqueSet());    // print [All!, Hello, Hi, World!]- in natural (alphabet) order


    // Print count occurrences of words
    System.out.println("Hello = " + bag.getCount("Hello"));    // print 2
    System.out.println("World = " + bag.getCount("World!"));    // print 2
    System.out.println("All = " + bag.getCount("All!"));    // print 1
    System.out.println("Hi = " + bag.getCount("Hi"));    // print 1
    System.out.println("Empty = " + bag.getCount("Empty"));    // print 0

    // Print count all words
    System.out.println(bag.size());    //print 6

    // Print count unique words
    System.out.println(bag.uniqueSet().size());    //print 4

2. Using TreeBag from Eclipse(GC):

    // Parse text to separate words
    String INPUT_TEXT = "Hello World! Hello All! Hi World!";
    // Create Multiset
    MutableSortedBag<String> bag =  TreeBag.newBag(Arrays.asList(INPUT_TEXT.split(" ")));

    // Print count words
    System.out.println(bag); // print [All!, Hello, Hello, Hi, World!, World!]- in natural order
    // Print all unique words
    System.out.println(bag.toSortedSet());    // print [All!, Hello, Hi, World!]- in natural order

    // Print count occurrences of words
    System.out.println("Hello = " + bag.occurrencesOf("Hello"));    // print 2
    System.out.println("World = " + bag.occurrencesOf("World!"));    // print 2
    System.out.println("All = " + bag.occurrencesOf("All!"));    // print 1
    System.out.println("Hi = " + bag.occurrencesOf("Hi"));    // print 1
    System.out.println("Empty = " + bag.occurrencesOf("Empty"));    // print 0

    // Print count all words
    System.out.println(bag.size());    //print 6

    // Print count unique words
    System.out.println(bag.toSet().size());    //print 4

3. Using LinkedHashMultiset from Guava:

    // Parse text to separate words
    String INPUT_TEXT = "Hello World! Hello All! Hi World!";
    // Create Multiset
    Multiset<String> multiset = LinkedHashMultiset.create(Arrays.asList(INPUT_TEXT.split(" ")));

    // Print count words
    System.out.println(multiset); // print [Hello x 2, World! x 2, All!, Hi]- in predictable iteration order
    // Print all unique words
    System.out.println(multiset.elementSet());    // print [Hello, World!, All!, Hi] - in predictable iteration order

    // Print count occurrences of words
    System.out.println("Hello = " + multiset.count("Hello"));    // print 2
    System.out.println("World = " + multiset.count("World!"));    // print 2
    System.out.println("All = " + multiset.count("All!"));    // print 1
    System.out.println("Hi = " + multiset.count("Hi"));    // print 1
    System.out.println("Empty = " + multiset.count("Empty"));    // print 0

    // Print count all words
    System.out.println(multiset.size());    //print 6

    // Print count unique words
    System.out.println(multiset.elementSet().size());    //print 4

More examples:

I. Apache Collection:

1. HashBag - order not defined
2. SynchronizedBag - concurrent and order not defined
3. SynchronizedSortedBag - - concurrent and sorted order
4. TreeBag - sorted order

II. GS / Eclipse Collection

5. MutableBag - order not defined
6. MutableSortedBag - sorted order

III. Guava

7. HashMultiset - order not defined
8. TreeMultiset - sorted order
9. LinkedHashMultiset - insertion order
10. ConcurrentHashMultiset - concurrent and order not defined

This multimap allows duplicate key-value pairs. JDK analogs are HashMap<K, List>, HashMap<K, Set> and so on.

Key's order	Value's order	Duplicate	Analog key	Analog value	Guava	Apache	Eclipse (GS) Collections	JDK
not defined	Insertion-order	yes	HashMap	ArrayList	ArrayListMultimap	MultiValueMap	FastListMultimap	HashMap<K, ArrayList<V>>
not defined	not defined	no	HashMap	HashSet	HashMultimap	MultiValueMap. multiValueMap( new HashMap<K, Set>(), HashSet.class);	UnifiedSetMultimap	HashMap<K, HashSet<V>>
not defined	sorted	no	HashMap	TreeSet	Multimaps. newMultimap( HashMap, Supplier <TreeSet>)	MultiValueMap.multiValueMap( new HashMap<K, Set>(), TreeSet.class)	TreeSortedSet- Multimap	HashMap<K, TreeSet<V>>
Insertion-order	Insertion-order	yes	LinkedHashMap	ArrayList	LinkedListMultimap	MultiValueMap. multiValueMap(new LinkedHashMap<K, List>(), ArrayList.class);		LinkedHashMap< K, ArrayList>
Insertion-order	Insertion-order	no	LinkedHashMap	LinkedHashSet	LinkedHashMultimap	MultiValueMap. multiValueMap(new LinkedHashMap<K, Set>(), LinkedHashSet.class)		LinkedHashMap<K, LinkedHashSet<V>>
sorted	sorted	no	TreeMap	TreeSet	TreeMultimap	MultiValueMap. multiValueMap( new TreeMap<K, Set>(),TreeSet.class)		TreeMap<K, TreeSet<V>>

Examples using Multimap

Task: Parse "Hello World! Hello All! Hi World!" string to separate words and print all indexes of every word using MultiMap (for example, Hello=[0, 2], World!=[1, 5] and so on)

1. MultiValueMap from Apache

    String INPUT_TEXT = "Hello World! Hello All! Hi World!";
    // Parse text to words and index
    List<String> words = Arrays.asList(INPUT_TEXT.split(" "));
    // Create Multimap
    MultiMap<String, Integer> multiMap = new MultiValueMap<String, Integer>();


    // Fill Multimap
    int i = 0;
    for(String word: words) {
        multiMap.put(word, i);
        i++;
    }

    // Print all words
    System.out.println(multiMap); // print {Hi=[4], Hello=[0, 2], World!=[1, 5], All!=[3]} - in random orders
    // Print all unique words
    System.out.println(multiMap.keySet());    // print [Hi, Hello, World!, All!] - in random orders

    // Print all indexes
    System.out.println("Hello = " + multiMap.get("Hello"));    // print [0, 2]
    System.out.println("World = " + multiMap.get("World!"));    // print [1, 5]
    System.out.println("All = " + multiMap.get("All!"));    // print [3]
    System.out.println("Hi = " + multiMap.get("Hi"));    // print [4]
    System.out.println("Empty = " + multiMap.get("Empty"));    // print null

    // Print count unique words
    System.out.println(multiMap.keySet().size());    //print 4

2. HashBiMap from GS / Eclipse Collection

    String[] englishWords = {"one", "two", "three","ball","snow"};
    String[] russianWords = {"jeden", "dwa", "trzy", "kula", "snieg"};

    // Create Multiset
    MutableBiMap<String, String> biMap = new HashBiMap(englishWords.length);
    // Create English-Polish dictionary
    int i = 0;
    for(String englishWord: englishWords) {
        biMap.put(englishWord, russianWords[i]);
        i++;
    }

    // Print count words
    System.out.println(biMap); // print {two=dwa, ball=kula, one=jeden, snow=snieg, three=trzy} - in random orders
    // Print all unique words
    System.out.println(biMap.keySet());    // print [snow, two, one, three, ball] - in random orders
    System.out.println(biMap.values());    // print [dwa, kula, jeden, snieg, trzy] - in random orders

    // Print translate by words
    System.out.println("one = " + biMap.get("one"));    // print one = jeden
    System.out.println("two = " + biMap.get("two"));    // print two = dwa
    System.out.println("kula = " + biMap.inverse().get("kula"));    // print kula = ball
    System.out.println("snieg = " + biMap.inverse().get("snieg"));    // print snieg = snow
    System.out.println("empty = " + biMap.get("empty"));    // print empty = null

    // Print count word's pair
    System.out.println(biMap.size());    //print 5

3. HashMultiMap from Guava

    String INPUT_TEXT = "Hello World! Hello All! Hi World!";
    // Parse text to words and index
    List<String> words = Arrays.asList(INPUT_TEXT.split(" "));
    // Create Multimap
    Multimap<String, Integer> multiMap = HashMultimap.create();
   
    // Fill Multimap
    int i = 0;
    for(String word: words) {
        multiMap.put(word, i);
        i++;
    }
   
    // Print all words
    System.out.println(multiMap); // print {Hi=[4], Hello=[0, 2], World!=[1, 5], All!=[3]} - keys and values in random orders
    // Print all unique words
    System.out.println(multiMap.keySet());    // print [Hi, Hello, World!, All!] - in random orders
   
    // Print all indexes
    System.out.println("Hello = " + multiMap.get("Hello"));    // print [0, 2]
    System.out.println("World = " + multiMap.get("World!"));    // print [1, 5]
    System.out.println("All = " + multiMap.get("All!"));    // print [3]
    System.out.println("Hi = " + multiMap.get("Hi"));    // print [4]
    System.out.println("Empty = " + multiMap.get("Empty"));    // print []
   
    // Print count all words
    System.out.println(multiMap.size());    //print 6
   
    // Print count unique words
    System.out.println(multiMap.keySet().size());    //print 4
   

Nore examples:

I. Apache Collection:

1. MultiValueMap
2. MultiValueMapLinked
3. MultiValueMapTree

II. GS / Eclipse Collection

1. FastListMultimap
2. HashBagMultimap
3. TreeSortedSetMultimap
4. UnifiedSetMultimap

III. Guava

1. HashMultiMap
2. LinkedHashMultimap
3. LinkedListMultimap
4. TreeMultimap
5. ArrayListMultimap

Compare operation with collections - Create collections

1. Create List

Description	JDK	guava	gs-collections
Create empty list	new ArrayList<>()	Lists.newArrayList()	FastList.newList()
Create list from values	Arrays.asList("1", "2", "3")	Lists.newArrayList("1", "2", "3")	FastList.newListWith("1", "2", "3")
Create list with capacity = 100	new ArrayList<>(100)	Lists.newArrayListWithCapacity(100)	FastList.newList(100)
Create list from any collectin	new ArrayList<>(collection)	Lists.newArrayList(collection)	FastList.newList(collection)
Create list from any Iterable	-	Lists.newArrayList(iterable)	FastList.newList(iterable)
Create list from Iterator	-	Lists.newArrayList(iterator)	-
Create list from array	Arrays.asList(array)	Lists.newArrayList(array)	FastList.newListWith(array)
Create list using factory	-	-	FastList.newWithNValues(10, () -> "1")

Examples:

    System.out.println("createArrayList start");
    // Create empty list
    List<String> emptyGuava = Lists.newArrayList(); // using guava
    List<String> emptyJDK = new ArrayList<>(); // using JDK
    MutableList<String>  emptyGS = FastList.newList(); // using gs

    // Create list with 100 element
    List < String > exactly100 = Lists.newArrayListWithCapacity(100); // using guava
    List<String> exactly100JDK = new ArrayList<>(100); // using JDK
    MutableList<String>  empty100GS = FastList.newList(100); // using gs

    // Create list with about 100 element
    List<String> approx100 = Lists.newArrayListWithExpectedSize(100); // using guava
    List<String> approx100JDK = new ArrayList<>(115); // using JDK
    MutableList<String>  approx100GS = FastList.newList(115); // using gs

    // Create list with some elements
    List<String> withElements = Lists.newArrayList("alpha", "beta", "gamma"); // using guava
    List<String> withElementsJDK = Arrays.asList("alpha", "beta", "gamma"); // using JDK
    MutableList<String>  withElementsGS = FastList.newListWith("alpha", "beta", "gamma"); // using gs

    System.out.println(withElements);
    System.out.println(withElementsJDK);
    System.out.println(withElementsGS);

    // Create list from any Iterable interface (any collection)
    Collection<String> collection = new HashSet<>(3);
    collection.add("1");
    collection.add("2");
    collection.add("3");

    List<String> fromIterable = Lists.newArrayList(collection); // using guava
    List<String> fromIterableJDK = new ArrayList<>(collection); // using JDK
    MutableList<String>  fromIterableGS = FastList.newList(collection); // using gs

    System.out.println(fromIterable);
    System.out.println(fromIterableJDK);
    System.out.println(fromIterableGS);
    /* Attention: JDK create list only from Collection, but guava and gs can create list from Iterable and Collection */

    // Create list from any Iterator
    Iterator<String> iterator = collection.iterator();
    List<String> fromIterator = Lists.newArrayList(iterator); // using guava
    System.out.println(fromIterator);

    // Create list from any array
    String[] array = {"4", "5", "6"};
    List<String> fromArray = Lists.newArrayList(array); // using guava
    List<String> fromArrayJDK = Arrays.asList(array); // using JDK
    MutableList<String>  fromArrayGS = FastList.newListWith(array); // using gs
    System.out.println(fromArray);
    System.out.println(fromArrayJDK);
    System.out.println(fromArrayGS);

    // Create list using fabric
    MutableList<String>  fromFabricGS = FastList.newWithNValues(10, () -> String.valueOf(Math.random())); // using gs
    System.out.println(fromFabricGS);

    System.out.println("createArrayList end");

2 Create Set

Description	JDK	guava	gs-collections
Create empty set	new HashSet<>()	Sets.newHashSet()	UnifiedSet.newSet()
Creatre set from values	new HashSet<>(Arrays.asList("alpha", "beta", "gamma"))	Sets.newHashSet("alpha", "beta", "gamma")	UnifiedSet.newSetWith("alpha", "beta", "gamma")
Create set from any collections	new HashSet<>(collection)	Sets.newHashSet(collection)	UnifiedSet.newSet(collection)
Create set from any Iterable	-	Sets.newHashSet(iterable)	UnifiedSet.newSet(iterable)
Create set from any Iterator	-	Sets.newHashSet(iterator)	-
Create set from Array	new HashSet<>(Arrays.asList(array))	Sets.newHashSet(array)	UnifiedSet.newSetWith(array)

Examples:

    System.out.println("createHashSet start");
    // Create empty set
    Set<String> emptyGuava = Sets.newHashSet(); // using guava
    Set<String> emptyJDK = new HashSet<>(); // using JDK
    Set<String> emptyGS = UnifiedSet.newSet(); // using gs

    // Create set with 100 element
    Set<String> approx100 = Sets.newHashSetWithExpectedSize(100); // using guava
    Set<String> approx100JDK = new HashSet<>(130); // using JDK
    Set<String> approx100GS = UnifiedSet.newSet(130); // using gs

    // Create set from some elements
    Set<String> withElements =  Sets.newHashSet("alpha", "beta", "gamma"); // using guava
    Set<String> withElementsJDK = new HashSet<>(Arrays.asList("alpha", "beta", "gamma")); // using JDK
    Set<String> withElementsGS  = UnifiedSet.newSetWith("alpha", "beta", "gamma"); // using gs

    System.out.println(withElements);
    System.out.println(withElementsJDK);
    System.out.println(withElementsGS);

    // Create set from any Iterable interface (any collection)
    Collection<String> collection = new ArrayList<>(3);
    collection.add("1");
    collection.add("2");
    collection.add("3");

    Set<String> fromIterable = Sets.newHashSet(collection); // using guava
    Set<String> fromIterableJDK = new HashSet<>(collection); // using JDK
    Set<String> fromIterableGS  = UnifiedSet.newSet(collection); // using gs

    System.out.println(fromIterable);
    System.out.println(fromIterableJDK);
    System.out.println(fromIterableGS);
    /* Attention: JDK create set only from Collection, but guava and gs can create set from Iterable and Collection */

    // Create set from any Iterator
    Iterator<String> iterator = collection.iterator();
    Set<String> fromIterator = Sets.newHashSet(iterator); // using guava
    System.out.println(fromIterator);

    // Create set from any array
    String[] array = {"4", "5", "6"};
    Set<String> fromArray = Sets.newHashSet(array); // using guava
    Set<String> fromArrayJDK = new HashSet<>(Arrays.asList(array)); // using JDK
    Set<String> fromArrayGS  = UnifiedSet.newSetWith(array); // using gs
    System.out.println(fromArray);
    System.out.println(fromArrayJDK);
    System.out.println(fromArrayGS);

    System.out.println("createHashSet end");

3 Create Map

Description	JDK	guava	gs-collections
Create empty map	new HashMap<>()	Maps.newHashMap()	UnifiedMap.newMap()
Create map with capacity = 130	new HashMap<>(130)	Maps.newHashMapWithExpectedSize(100)	UnifiedMap.newMap(130)
Create map from other map	new HashMap<>(map)	Maps.newHashMap(map)	UnifiedMap.newMap(map)
Create map from keys	-	-	UnifiedMap.newWithKeysValues("1", "a", "2", "b")

Examples:

    System.out.println("createHashMap start");
    // Create empty map
    Map<String, String> emptyGuava = Maps.newHashMap(); // using guava
    Map<String, String> emptyJDK = new HashMap<>(); // using JDK
    Map<String, String> emptyGS = UnifiedMap.newMap(); // using gs

    // Create map with about 100 element
    Map<String, String> approx100 = Maps.newHashMapWithExpectedSize(100); // using guava
    Map<String, String> approx100JDK = new HashMap<>(130); // using JDK
    Map<String, String> approx100GS = UnifiedMap.newMap(130); // using gs

    // Create map from another map
    Map<String, String> map = new HashMap<>(3);
    map.put("k1","v1");
    map.put("k2","v2");
    Map<String, String> withMap =  Maps.newHashMap(map); // using guava
    Map<String, String> withMapJDK = new HashMap<>(map); // using JDK
    Map<String, String> withMapGS = UnifiedMap.newMap(map); // using gs

    System.out.println(withMap);
    System.out.println(withMapJDK);
    System.out.println(withMapGS);

    // Create map from keys
    Map<String, String> withKeys =  UnifiedMap.newWithKeysValues("1", "a", "2", "b");
    System.out.println(withKeys);

    System.out.println("createHashMap end");

More examples: CreateCollectionTest

1. CollectionCompare
2. CollectionSearch
3. JavaTransform