HashMap: iterating the key-value pairs in random order

Question

I have a HashMap and I\'d like to iterate they key-value pairs in a different random order each time i get the iterator. Conceptually I\'d like to \"shuffle\" the map before

Answer 1

Reshuffling a large collection is always going to be expensive. You are going to need at least one reference per entry. e.g. for 1 million entries you will need approx 4 MB.

Note; the shuffle operation is O(N)

I would use

Map map = 
List> list = new ArrayList>(map.entrySet());

// each time you want a different order.
Collections.shuffle(list);
for(Map.Entry entry: list) { /* ... */ }