LinkedHashMap

1. What is LinkedHashMap?

LinkedHashMap is a variation of HashMap that maintains the insertion order of key-value pairs, meaning entries appear in the exact order they were added.

2. Why is it used?

It's useful when you need the fast lookup benefits of a HashMap, but also want the entries to appear in a predictable, consistent order — for example, when displaying recently added items in the order they were added.

3. Real-Life Example

Think of a reception logbook where visitor entries are recorded strictly in the order they arrive, even though each visitor also has a unique ID for lookup. LinkedHashMap preserves this same kind of arrival order.

4. Syntax

java
LinkedHashMap<KeyType, ValueType> mapName = new LinkedHashMap<>();

5. Example Program

java
import java.util.LinkedHashMap;

public class LinkedHashMapDemo {
    public static void main(String[] args) {
        LinkedHashMap<String, Integer> scores = new LinkedHashMap<>();
        scores.put("Ankit", 70);
        scores.put("Meera", 95);
        System.out.println(scores);
    }
}

Output:

{Ankit=70, Meera=95}

6. Key Points to Remember

• LinkedHashMap preserves insertion order, unlike HashMap.
• It's slightly slower than HashMap due to the extra bookkeeping needed to maintain order.
• It can also be configured to maintain access order instead of insertion order, useful for building simple caches.