Each element must be unique Duplicate elements must not replace old elements. Elements are not key/value pairs. Accessing an element can be almost as fast as performing a similar operation on an array. Which of these classes provide the specified features?

  1. LinkedList

  2. TreeMap

  3. HashMap

  4. HashSet


Correct Option: D
Explanation:

To solve this question, the user needs to know the characteristics of different Java classes and their features.

  • LinkedList: This class provides an implementation of the List interface using a doubly-linked list. It allows duplicate elements and maintains the order of insertion. However, accessing an element in a LinkedList is slower than accessing an element in an array.

  • TreeMap: This class provides a red-black tree-based implementation of the SortedMap interface. It does not allow duplicate keys but allows duplicate values. It maintains the order of elements based on their natural ordering or a Comparator. Accessing an element in a TreeMap is slower than accessing an element in an array.

  • HashMap: This class provides a hash table-based implementation of the Map interface. It does not allow duplicate keys or values. It does not maintain the order of elements. Accessing an element in a HashMap is almost as fast as accessing an element in an array.

  • HashSet: This class provides a hash table-based implementation of the Set interface. It does not allow duplicate elements. It does not maintain the order of elements. Accessing an element in a HashSet is almost as fast as accessing an element in an array.

Based on the given features, the class that provides all the specified features is:

The Answer is: D, HashSet.

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