ArrayList as key in HashMap

Question

Would it be possible to add an ArrayList as the key of HashMap. I would like to keep the frequency count of bigrams. The bigram is the key and the

Answer 1

Unlike Array, List can be used as the key of a HashMap, but it is not a good idea, since we should always try to use an immutable object as the key.

.toString() method getting the String represtenation is a good key choice in many cases, since String is an immuteable object and can prefectly stands for the array or list.