Java LinkedHashMap Class

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Introduction

The Java LinkedHashMap class is Hash table and Linked list implementation of the Map interface, with predictable iteration order. Following are the important points about LinkedHashMap −

• The class provides all of the optional Map operations, and permits null elements.

• The Iteration over a HashMap is likely to be more expensive.

Class declaration

Following is the declaration for java.util.LinkedHashMap class −

public class LinkedHashMap<K,V>
   extends HashMap<K,V>
   implements Map<K,V>

Parameters

Following is the parameter for java.util.LinkedHashMap class −

• K − This is the type of keys maintained by this map.

• V − This is the the type of mapped values.

Class constructors

Sr.No.	Constructor & Description
1	LinkedHashMap() This constructs an empty insertion-ordered LinkedHashMap instance with the default initial capacity (16) and load factor (0.75).
2	LinkedHashMap(int initialCapacity) This constructs an empty insertion-ordered LinkedHashMap instance with the specified initial capacity and a default load factor (0.75).
3	LinkedHashMap(int initialCapacity, float loadFactor) This constructs an empty insertion-ordered LinkedHashMap instance with the specified initial capacity and load factor.
4	LinkedHashMap(int initialCapacity, float loadFactor, boolean accessOrder) This constructs an empty LinkedHashMap instance with the specified initial capacity, load factor and ordering mode.
5	LinkedHashMap(Map<? extends K,? extends V> m) This constructs an insertion-ordered LinkedHashMap instance with the same mappings as the specified map.

Class methods

Sr.No.	Method & Description
1	boolean containsValue(Object value) This method returns true if this map maps one or more keys to the specified value.
2	Set<Map.Entry<K,​V>> entrySet() This method returns a Set view of the mappings contained in this map.
3	V get​(Object key) This method returns the value to which the specified key is mapped, or null if this map contains no mapping for the key.
4	Set<K> keySet() This method returns a Set view of the keys contained in this map.
5	Collection<V> values() This method returns a Collection view of the values contained in this map.

Methods inherited

This class inherits methods from the following classes −

• java.util.HashMap
• java.util.AbstarctMap
• java.util.Object
• java.util.Map

Getting a Value from LinkedHashMap Example

The following example shows the usage of Java LinkedHashMap get() method to get a value based on a key from a Map. We've created a Map object of Integer,Integer. Then few entries are added, map is printed. Using get() method, a value is retrieved and printed.

package com.tutorialspoint;

import java.util.LinkedHashMap;

public class LinkedHashMapDemo {
   public static void main(String args[]) {
      
      // create hash map
      LinkedHashMap<Integer,Integer> newmap = new LinkedHashMap<>();

      // populate hash map
      newmap.put(1, 1);
      newmap.put(2, 2);
      newmap.put(3, 3); 

      System.out.println("Initial map elements: " + newmap);

      System.out.println("Value: " + newmap.get(1));
   }    
}

Output

Let us compile and run the above program, this will produce the following result.

Initial map elements: {1=1, 2=2, 3=3}
Value: 1