Java LinkedHashMap Class

Previous
Quiz
Next

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
Print Page
Previous
Next
Advertisements