Which method can be used to iterate over just the keys of a HashMap?

• A. map.values()
• B. map.keySet()
• C. map.entrySet()
• D. map.getAll()

Answer: (B)

The method that can be used to iterate over just the keys of a HashMap is indeed the one that involves the keySet() method. This method returns a Set view of the keys contained in the map, allowing you to iterate through them directly. By using keySet(), you can efficiently access all the unique keys stored in the HashMap, making it ideal for scenarios where you need to process or analyze the keys without considering the corresponding values.

The keySet() method ensures that any changes made to the map are reflected in the returned set and vice versa, maintaining synchronization between the two. This is particularly useful when you want to ensure that your operations on the keys take into account any additions or removals from the HashMap.

In contrast, the other methods provide different functionalities and do not focus solely on the keys. The values() method returns a Collection view of the values in the map, which is not what is needed for key iteration. The entrySet() method returns a Set of the key-value mappings, which means you would have to extract keys from entries, whereas map.getAll() is not a standard method in Java's HashMap class and is therefore not applicable.