Difference between HashMap and LinkedHashMap in java?

Question

Difference  between HashMap and LinkedHashMap in java?

Vulpes · Answer

Sure, here's one:
// HashMapDemo.java
import java.util.*;
class HashMapDemo {    public static void main(String[] args)    {         // create HashMap
HashMap hm = new HashMap ();
// put elements
hm.put("Barack Obama", "USA");        hm.put("David Cameron", "UK");        hm.put("Pranab Mukherjee", "India");                // print them out
for (Map.Entry entry : hm.entrySet())         {           System.out.println(entry.getKey() + " : " + entry.getValue());        }
System.out.println();
// create LinkedHashMap        LinkedHashMap lhm = new LinkedHashMap ();
// put elements
lhm.put("Barack Obama", "USA");        lhm.put("David Cameron", "UK");        lhm.put("Pranab Mukherjee", "India");
// print them out
for (Map.Entry entry : lhm.entrySet())         {           System.out.println(entry.getKey() + " : " + entry.getValue());        }     } }
The output is:
David Cameron : UK Barack Obama : USA Pranab Mukherjee : India
Barack Obama : USA David Cameron : UK Pranab Mukherjee : India
Notice that in the case of LinkedHashMap, the entries are iterated in the order they were added but this is not so in the case of HashMap.

Abhijeet Singh · Answer

Sir,
Please Explain with example?

Vulpes · Answer

The difference is that the LinkedHashMap enables you to iterate through the elements of the map in the order in which they were inserted.
In the case of the HashMap class, there is no guarantee that this will be the case - the order in which the elements are returned by an iteration will not necessarily be the same as the order in which they were added.