Master Java LinkedHashMap: Creation, Operations, and Performance Comparison

Master Java LinkedHashMap: Creation, Operations, and Performance Comparison

Discover how to create, manipulate, and compare Java’s LinkedHashMap with real-world examples and best practices.

The LinkedHashMap class in Java’s collections framework combines the fast lookups of a hash table with a predictable iteration order, thanks to an internal doubly-linked list that preserves insertion or access order.

Creating a LinkedHashMap

To use a LinkedHashMap, import java.util.LinkedHashMap and instantiate it. The constructor accepts initial capacity, load factor, and an optional accessOrder flag.

// LinkedHashMap with initial capacity 8 and load factor 0.6
LinkedHashMap<Key, Value> numbers = new LinkedHashMap<>(8, 0.6f);

Parameters:

• capacity – the number of buckets; default is 16.
• loadFactor – triggers resizing when the table is 60% full; default is 0.75.
• accessOrder – false for insertion order, true for least‑to‑most recent access order.

Example with default settings:

LinkedHashMap<Key, Value> defaultMap = new LinkedHashMap<>();

Creating a LinkedHashMap from Existing Maps

Copy an existing map into a LinkedHashMap to preserve order:

LinkedHashMap<String, Integer> evenNumbers = new LinkedHashMap<>();
evenNumbers.put("Two", 2);
evenNumbers.put("Four", 4);

LinkedHashMap<String, Integer> numbers = new LinkedHashMap<>(evenNumbers);
numbers.put("Three", 3);

Output:

LinkedHashMap1: {Two=2, Four=4}
LinkedHashMap2: {Two=2, Four=4, Three=3}

Key Operations

Insert Elements

• put(key, value) – add or replace a mapping.
• putIfAbsent(key, value) – add only if the key is missing.
• putAll(map) – merge another map.

LinkedHashMap<String, Integer> numbers = new LinkedHashMap<>();
numbers.put("One", 1);
numbers.putIfAbsent("Two", 2);
numbers.putAll(evenNumbers);

Access Elements

Retrieve keys, values, or entries:

• entrySet() – all key/value pairs.
• keySet() – all keys.
• values() – all values.
• get(key) – value or null if missing.
• getOrDefault(key, default) – safe retrieval with a fallback.

int val = numbers.get("Three");
int def = numbers.getOrDefault("Five", 5);

Remove Elements

• remove(key) – delete by key.
• remove(key, value) – delete only if the value matches.
• clear() – wipe the map.
• containsKey(key) – existence check.
• containsValue(value) – existence check.
• size() – number of entries.
• isEmpty() – emptiness check.

LinkedHashMap vs. HashMap

• LinkedHashMap preserves insertion or access order; HashMap does not.
• LinkedHashMap uses extra memory for node links.
• LinkedHashMap’s iteration is slightly slower but offers predictable ordering.