Does HashMap provide instant access to elements by value in all cases?

HashMap provides quick access to elements by key, not by value. The time to access an element by key is usually close to O(1), but searching by value requires iterating over all elements, which takes O(n).

Therefore, HashMap does not provide instant access by value in any case. If you need to search quickly by value, you should use an additional data structure, such as a reverse map (value -> key) or specialized collections.

Example:

HashMap<Integer, String> map = new HashMap<>();
map.put(1, "apple");
map.put(2, "banana");

// Fast access by key
String fruit = map.get(1); // "apple"

// Search by value
boolean hasBanana = map.containsValue("banana"); // requires iteration