HashSet vs ArrayList contains performance

Question

When processing large amounts of data I often find myself doing the following:

HashSet set = new HashSet ();
//Adding elements to         


        

Answer 1

The ArrayList uses an array for storing the data. The ArrayList.contains will be of O(n) complexity. So essentially searching in array again and again will have O(n^2) complexity.

While HashSet uses hashing mechanism for storing the elements into their respective buckets. The operation of HashSet will be faster for long list of values. It will reach the element in O(1).