Can you explain the mechanism of adding elements to the HashSet data structure?

HashSet in Java (and Android) is implemented based on HashMap. When you add an element to HashSet, the following happens:

1. The hash code of the element is computed using the hashCode() method.
2. The index of the bucket in the internal array is determined by the hash code.
3. If there are already elements in the bucket, a comparison is made using equals() to check if the element already exists (to avoid duplicates).
4. If the element is not present, it is added to the bucket.

Thus, HashSet ensures element uniqueness and quick access through hashing.

Example of adding:

HashSet<String> set = new HashSet<>();
set.add("apple");
set.add("banana");
set.add("apple"); // will not be added, as "apple" already exists