LinkedHashMap in Java

LinkedHashMap is a HashMap that also maintains a doubly-linked list connecting all entries in insertion order. Every get, put, and iteration runs in O(1) — same as HashMap — but the iteration order is predictable.

Use LinkedHashMap when you need fast key-value lookup AND you want entries to come out in the order you put them in.

Basic Usage — Insertion Order Maintained

Run this example to see its output.

Line by line:

• Entries print in insertion order — Biryani, Dosa, Paneer Tikka, Lassi.
• Updating an existing key does not change its position in the order.
• HashMap would print in unpredictable order; LinkedHashMap never does.

Comparing HashMap vs LinkedHashMap vs TreeMap

Run this example to see its output.

Simple LRU Cache Pattern

LinkedHashMap supports an access order mode — recently accessed entries move to the end. Combined with overriding removeEldestEntry(), you get a simple LRU (Least Recently Used) cache.

Run this example to see its output.

user:2 was the least recently used, so it gets evicted when the 4th entry is added. This is the LRU pattern — exactly what database and web caches use.

Common Mistake: Expecting Same Order as TreeMap

LinkedHashMap preserves the order you inserted. It does not sort.

Practice Task

Task: Simulate a simple browser history using LinkedHashMap<String, String> (URL → page title). Visit 5 pages. Then print the history in visit order. Remove one page from the middle. Print the remaining history.

Hint: remove("url") removes by key. Iterate with entrySet() to print both URL and title.

Solution:

Run this example to see its output.

What to observe: History prints in visit order every time — guaranteed by LinkedHashMap. Change to HashMap — the order becomes random. Change to TreeMap — the order becomes alphabetical by URL, not visit order.