Insertion order in LinkedHashMap using java (with example)

LinkedHashMap has following attributes.

• LinkedHashMap maintains the insertion order.
  • The default mode is insertion order.
  • The order in which elements are added to LinkedHashMap, is maintained
• LinkedHashMap is Hashtable and LinkedList based implementation of Map interface.

Constructors of LinkedHashMap are as follows:

• LinkedHashMap()
  Constructs an empty insertion-ordered LinkedHashMap instance with the default initial capacity (16) and load factor (0.75).
• LinkedHashMap(int initialCapacity)
  Constructs an empty insertion-ordered LinkedHashMap instance with the specified initial capacity and a default load factor (0.75).
• LinkedHashMap(int initialCapacity, float loadFactor)
  Constructs an empty insertion-ordered LinkedHashMap instance with the specified initial capacity and load factor.
• LinkedHashMap(int initialCapacity, float loadFactor, boolean accessOrder)
  Constructs an empty LinkedHashMap instance with the specified initial capacity, load factor and ordering mode.
• LinkedHashMap(Map<? extends K,? extends V> m)
  Constructs an insertion-ordered LinkedHashMap instance with the same mappings as the specified map.

Program –  Insertion order of LinkedHashMap in java

package org.learn.collection.map.lhashmap;

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

public class DemoInsertionOrderLinkedHashMap {

 public static void main(String[] args) {
  Map<Integer, String> mapVehicleNoAndOwner = new LinkedHashMap<>(2,0.75f);
  
  mapVehicleNoAndOwner.put(1000, "Federer");
  mapVehicleNoAndOwner.put(2000, "Bradman");
  mapVehicleNoAndOwner.put(3000, "Jordan");
  mapVehicleNoAndOwner.put(4000, "Woods");
  mapVehicleNoAndOwner.put(5000, "Ali");
  
  System.out.println("1. Iterating LinkedHashMap: ");
  demoIterate_InsertionOrder(mapVehicleNoAndOwner);  
  int key = 1000;
  System.out.printf("2. Accessting value at key: %d is %s\n",key,mapVehicleNoAndOwner.get(key));
  
  key = 3000;
  System.out.printf("3. Accessting value at key: %d is %s\n",key,mapVehicleNoAndOwner.get(key));
  
  System.out.println("4. Iterating LinkedHashMap, insertion order maintained: ");
  demoIterate_InsertionOrder(mapVehicleNoAndOwner);
  
 }

 private static void demoIterate_InsertionOrder(Map<Integer, String> mapVehicleNoAndOwner) {

  mapVehicleNoAndOwner.forEach((key, value) -> {
   System.out.println("Key:"+ key + ", Value:" + value);
  });  
 }
}

Output –  Insertion order of LinkedHashMap in java

1. Iterating LinkedHashMap: 
Key:1000, Value:Federer
Key:2000, Value:Bradman
Key:3000, Value:Jordan
Key:4000, Value:Woods
Key:5000, Value:Ali
2. Accessting value at key: 1000 is Federer
3. Accessting value at key: 3000 is Jordan
4. Iterating LinkedHashMap, insertion order maintained: 
Key:1000, Value:Federer
Key:2000, Value:Bradman
Key:3000, Value:Jordan
Key:4000, Value:Woods
Key:5000, Value:Ali