Question

Is there an implementation of the java Map interface which utilizes separate chaining as collision resolution. By reading the javadocs for HashMap and HashTable I came to the conclusion that what the implementation does is basically replace the value and essentially doesn’t employ any collision resolution?

Answer 1

You got it wrong: it uses a linked list of entries for each bucket.

When putting a value in the map, the map starts by calling hashCode on the key, then transforms this hash code so that it’s between 0 and the number of buckets. If the bucket is empty, the key is stored in this bucket. If it’s not, then every key in this bucket is compared to the new key with equals. If one is equal, then its value is replaced by the new value. Else, a new entry with the new key is added to the bucket’s list of entries.

If you want to store multiple values for a given key, then use a Map<Key, List<Value>>, or use Guava’s MultiMap.