Is it possible to store a list of elements inside a single bucket in a HashMap?

In the standard implementation of HashMap in Java or Kotlin, each bucket (bin) stores a chain of elements that have the same hash code (collisions). However, you cannot directly manage buckets and store a list of elements in one bucket — this is an internal implementation.

If you need to store a list of elements under a single key, you can use a HashMap with a key and a value of type List or MutableList. For example:

val map = HashMap<String, MutableList<Int>>()

// Add an element to the list under a key
map.getOrPut("key") { mutableListOf() }.add(42)

Thus, you store a list of elements inside a single key, not inside a single hash table bucket.