How is data retrieved by key from a HashMap structure?

Data retrieval by key from HashMap in Java occurs in several steps:

1. The hash code of the key is computed using the hashCode() method.
2. The hash code is further processed (for example, using bitwise operations) to determine the index of the bucket in the array.
3. In the selected bucket, a search is performed for an element with a key equal to the sought one (comparison via equals()).
4. If such an element is found, its associated value is returned.

Example:

HashMap<String, Integer> map = new HashMap<>();
map.put("apple", 5);

Integer value = map.get("apple"); // value will be 5

Thus, access to the element occurs in amortized constant time O(1), assuming the hash function distributes keys evenly.