How to Implement a Map with Duplicate Keys in Java?

Multimap Implementation for Duplicate Keys

The original question sought a map implementation that allows duplicate keys. While there are numerous map implementations, this specific requirement calls for a multimap. Multimaps, available in both Apache Commons Collections and Google Guava, address this need by maintaining a collection of values for each key.

In other words, in a multimap, you can associate an object with multiple keys, and when you retrieve the object, you obtain a collection of all the keys associated with it.

For Java 5 and later, Guava's Multimap is a recommended choice due to its generics support. By leveraging this feature, you can specify the types of keys and values stored in the multimap, providing a type-safe and easier-to-use API.

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