Implementation of Multimap that does not allow duplicate key-value entries and that returns collections whose iterators follow the ordering in which the data was added to the multimap.

The collections returned by keySet, keys, and asMap iterate through the keys in the order they were first added to the multimap. Similarly, get, removeAll, and replaceValues return collections that iterate through the values in the order they were added. The collections generated by entries and values iterate across the key-value mappings in the order they were added to the multimap.

The iteration ordering of the collections generated by keySet, keys, and asMap has a few subtleties. As long as the set of keys remains unchanged, adding or removing mappings does not affect the key iteration order. However, if you remove all values associated with a key and then add the key back to the multimap, that key will come last in the key iteration order.

The multimap does not store duplicate key-value pairs. Adding a new key-value pair equal to an existing key-value pair has no effect.

Keys and values may be null. All optional multimap methods are supported, and all returned views are modifiable.

This class is not threadsafe when any concurrent operations update the multimap. Concurrent read operations will work correctly. To allow concurrent update operations, wrap your multimap with a call to Multimaps#synchronizedSetMultimap.

See the Guava User Guide article on Multimap.