Question

Which of the following stores key-value pairs and supports faster insertion and deletion? a. HashMap b. LinkedHashMap c. TreeMap d. None of the above

Short answer

HashMap

Step-by-step solution

Evaluate the Options

Review the given options: HashMap, LinkedHashMap, TreeMap, and None of the above. Figure out which data structure best supports faster insertion and deletion.

Properties of HashMap

HashMap stores key-value pairs and provides constant-time complexity (O(1)) for insertion and deletion due to hashing. It does not maintain order.

Properties of LinkedHashMap

LinkedHashMap is similar to HashMap but maintains insertion order with a doubly-linked list. The insertion and deletion operations have slightly higher complexity due to this added structure.

Properties of TreeMap

TreeMap stores key-value pairs and maintains a sorted order using a Red-Black tree, which takes O(log n) time for insertion and deletion, making it slower compared to HashMap.

Conclusion

Analyzing the properties and complexities, HashMap is the data structure that best supports faster insertion and deletion among the given options.

Key concepts

HashMap

A HashMap in Java is a part of the Collections Framework that stores key-value pairs.
It is highly efficient for insertion and deletion operations.
Let's take a closer look at some of its key aspects.

• Constant-Time Complexity: Due to its underlying hash table, HashMap offers O(1) time complexity for insertion and deletion operations, assuming good hash distribution and no collisions.
• Uniqueness and Nulls: HashMap keys must be unique. You can have one `null` key and multiple `null` values.
• No Order: HashMap does not maintain any order for its elements. The order can change as entries are added or removed.

Because of these properties, HashMap is often the go-to choice when fast insertion and deletion are crucial.

LinkedHashMap

LinkedHashMap extends the functionality of HashMap by maintaining a linked list of the entries.
This extra structure allows it to maintain insertion order.

• Insertion Order: LinkedHashMap keeps track of the order in which keys were inserted. This makes it useful for applications where iteration order matters.
• Time Complexity: Though slightly less performant than HashMap, it still offers O(1) time complexity for basic operations like insertion and deletion.
• Inheritance: It inherits the behavior of HashMap, including the ability to store `null` values and one `null` key.

If you need a combination of HashMap's performance and a predictable iteration order, LinkedHashMap is the right choice.

TreeMap

TreeMap is another map implementation in Java's Collections Framework.
It stores key-value pairs in a sorted order.
Let's explore its characteristics.

• Sorted Order: Unlike HashMap and LinkedHashMap, TreeMap sorts its entries by natural order of keys or using a specified comparator.
• Time Complexity: TreeMap uses a Red-Black tree, resulting in O(log n) time complexity for insertion, deletion, and lookup operations.
• Null Handling: TreeMap does not allow `null` keys. Attempting to insert a `null` key will throw a `NullPointerException`, though `null` values are permitted.

If you need a map that maintains sorted key order and can tolerate the slightly lower performance, TreeMap is an excellent choice.