LinkedHashMap class extends the HashMap class and implements Map Interface to store values in key and value pairs.

Points to Remember

• LinkedHashMap class is in java.util package.
• LinkedHashMap uses data structure Hashtable and LinkedList implementation of the Map interface.
• LinkedHashMap contains values based on the key.
• LinkedHashMap contains unique elements.
• LinkedHashMap class may have one null key and multiple null values.
• LinkedHashMap is not synchronized.
• LinkedHashMap maintains the insertion order.
• LinkedHashMap initial default capacity is 16 with a load factor of 0.75.

LinkedHashMap Declaration

public class LinkedHashMap extends HashMap implements Map  

• K: Here K represent Key of Map
• V: Here V represents value in the Map with respect to K.

Constructors of LinkedHashMap class

Constructor	Description
LinkedHashMap()	This is the default LinkedHashMap constructor.
LinkedHashMap(int capacity)	Use to initialize a LinkedHashMap with the given capacity.
LinkedHashMap(int capacity, float loadFactor)	Use to initialize both the capacity and the load factor.
LinkedHashMap(int capacity, float loadFactor, boolean accessOrder)	Use to initialize both the capacity and the load factor with specified ordering mode.
LinkedHashMap(Map m)	Use to initialize the LinkedHashMap with the elements from the given Map class m.

Methods of LinkedHashMap class

Method	Description
V get(Object key)	It returns the value object map to the specified key.
void clear()	It removes all the key-value pairs from a map.
boolean containsValue(Object value)	It returns true if one or more keys to the specified value.
Set<Map.Entry> entrySet()	It returns a Set view of the mappings contained in the map.
void forEach(BiConsumer action)	It performs the given action on each entry in the map until all entries have been processed or any action throws an exception.
V getOrDefault(Object key, V defaultValue)	It returns the value to which the specified key is mapped or defaultValue if this map contains no mapping for the key.
Set keySet()	It returns a Set view of the keys contained in the map
protected boolean removeEldestEntry(Map.Entry eldest)	It returns true on removing its eldest entry.
void replaceAll(BiFunction function)	It replaces each entry’s value in map with the result of invoking the given function on that entry until all entries have been processed or the function throws an exception.
Collection values()	It returns a Collection view of the values contained in this map.

LinkedHashMap Example : insert items and traverse

import java.util.LinkedHashMap;
import java.util.Map;

public class LinkedHashMapExample4 {

	public static void main(String args[]) {

		Map hm = new LinkedHashMap();

		hm.put(20, "Anuj");
		hm.put(21, "Virendra");
		hm.put(22, "Raghav");

		for (Map.Entry m : hm.entrySet()) {
			System.out.println(m.getKey() + " " + m.getValue());
		}
	}

}

Output :

20 Anuj
21 Virendra
22 Raghav

LinkedHashMap Example : Key-Value pair

import java.util.LinkedHashMap;
import java.util.Map;

public class LinkedHashMapExample1 {

	public static void main(String args[]) {
		Map map = new LinkedHashMap();
		map.put(20, "Anuj");
		map.put(21, "Virendra");
		map.put(22, "Raghav");
		// Fetching key from LinkedHashMap
		System.out.println("Keys: " + map.keySet());
		// Fetching value from LinkedHashMap
		System.out.println("Values: " + map.values());
		// Fetching key-value pair from LinkedHashMap
		System.out.println("Key-Value pairs: " + map.entrySet());
	}

}

Output :

Keys: [20, 21, 22]
Values: [Anuj, Virendra, Raghav]
Key-Value pairs: [20=Anuj, 21=Virendra, 22=Raghav]

LinkedHashMap Example : remove()

import java.util.LinkedHashMap;
import java.util.Map;

public class LinkedHashMapExample2 {

	public static void main(String args[]) {
		Map map = new LinkedHashMap();
		map.put(20, "Anuj");
		map.put(22, "Ravi");
		map.put(21, "Virendra");
		map.put(23, "Raghav");
		System.out.println("Before remove: " + map);
		// Remove value for key 22
		map.remove(22);
		System.out.println("After remove: " + map);
	}

}

Output :

Before remove: {20=Anuj, 22=Ravi, 21=Virendra, 23=Raghav}
After remove: {20=Anuj, 21=Virendra, 23=Raghav}

LinkedHashMap Example : getOrDefault()

import java.util.LinkedHashMap;
import java.util.Map;

public class LinkedHashMapExample3 {

	public static void main(String args[]) {
		Map map = new LinkedHashMap();
		map.put(20, "Anuj");
		map.put(22, "Ravi");
		map.put(21, "Virendra");
		map.put(23, "Raghav");
		// Here it will retrieve values for key 21 and 25
		// if values not find out in HashTable then return default value
		System.out.println(map.getOrDefault(21, "Not Found"));
		System.out.println(map.getOrDefault(25, "Not Found"));
	}
}

Output :

Virendra
Not Found

LinkedHashMap Example : with objects

import java.util.*;
class Magzine{
int id;
String name,author,publisher;
int quantity;
public Magzine(int id, String name, String author, String publisher, int quantity) {
    this.id = id;
    this.name = name;
    this.author = author;
    this.publisher = publisher;
    this.quantity = quantity;
}
}
public class LinkedHashMapExampleWithObjects {
	public static void main(String[] args) {
		// Creating map of Magzine
		Map map = new LinkedHashMap();
		// Creating Magzines
		Magzine m1 = new Magzine(21, "The Sun", "Sy Sunfranchy", "The Sun Company", 8);
		Magzine m2 = new Magzine(22, "Glimmer Trains", "Unknown", "Glimmer Train Press", 4);
		Magzine m3 = new Magzine(23, "Crazy horse", "Brett Lot", "College of Charleston", 6);

		// Adding magzine to map
		map.put(1, m1);
		map.put(2, m2);
		map.put(3, m3);
		// Traversing map
		for (Map.Entry entry : map.entrySet()) {
			int key = entry.getKey();
			Magzine m = entry.getValue();
			System.out.println("\nId: "+key + " Details:");
			System.out.println(m.id + " " + m.name + " " + m.author + " " + m.publisher + " " + m.quantity);
		}
	}
}

Output :

Id: 1 Details:
21 The Sun Sy Sunfranchy The Sun Company 8

Id: 2 Details:
22 Glimmer Trains Unknown Glimmer Train Press 4

Id: 3 Details:
23 Crazy horse Brett Lot College of Charleston 6