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I see many examples about multimap but did not understand why Google Gauva is different?
Multimap<Integer, Set<String>> option4 = HashMultimap.create(); // Gauva Map<Integer, Set<String>> opt = new HashMap<Integer, Set<String>>(); //Core Java Is both above are behave same for holding data or different?
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HashMap is a non-synchronized class of the Java Collection Framework that contains null values and keys, whereas Map is a Java interface, which is used to map key-pair values.
HashMap is non-syncronized and is not thread safe while HashTable is thread safe and is synchronized. HashMap allows one null key and values can be null whereas HashTable doesn't allow null key or value. HashMap is faster than HashTable. HashMap iterator is fail-safe where HashTable iterator is not fail-safe.
HashMap Stores elements in form of key-value pair i.e each element has its corresponding key which is required for its retrieval during iteration. HashSet stores only objects no such key value pairs maintained. Put method of hash map is used to add element in hashmap.
ArrayList stores the elements only as values and maintains internally the indexing for every element. While HashMap stores elements with key and value pairs that means two objects. So HashMap takes more memory comparatively.
A MultiMap<A, B> associates a key of type A with a value of type Collection<B> (hence the name MultiMap)
A Map<A, B> associates a key of type A with a value of type B.
So, a MultiMap<Integer, Set<String>> can be viewed as a Map<Integer, Collection<Set<String>>. This should be obvious by reading the api documentation.
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