Map maintaining insert order of key-value pairs

Many time we want to maintain order of entries as it is inserted. HashMap does not satisfy this requirement. For all such requirement java collection framework has provided LinkedHashMap.

Following example explains :

  1: import java.util.*;
  2: class MapTest 
  3: {
  4: 	public static void main(String[] args) 
  5: 	{
  6: 		System.out.println("Using HashMap:");
  7: 		Map hashMap = new HashMap();
  8: 		hashMap.put("One","One");
  9: 		hashMap.put("Two","Two");
 10: 		hashMap.put("Three","Three");
 11: 		hashMap.put("Four","Four");
 12: 		hashMap.put("Five","Five");
 13: 		System.out.println("Complete Map content : "+ hashMap.toString());
 14: 		System.out.println("Iterating Key-Value:");
 15: 		Iterator itr = hashMap.keySet().iterator();
 16: 		while(itr.hasNext()){
 17: 			System.out.println(hashMap.get(itr.next()));
 18: 		}
 19: 
 20: 		System.out.println("\nUsing LinkedHashMap:");
 21: 		LinkedHashMap map = new LinkedHashMap();
 22: 		map.put("One","One");
 23: 		map.put("Two","Two");
 24: 		map.put("Three","Three");
 25: 		map.put("Four","Four");
 26: 		map.put("Five","Five");
 27: 		System.out.println("Complete Map content : "+ map.toString());
 28: 		System.out.println("Iterating Key-Value:");
 29: 		itr = map.keySet().iterator();
 30: 		while(itr.hasNext()){
 31: 			System.out.println(map.get(itr.next()));
 32: 		}
 33: 		System.out.println("End of Main");
 34: 	}

Output :

---------- java ----------
Using HashMap:
Complete Map content : {Five=Five, Three=Three, One=One, Four=Four, Two=Two}
Iterating Key-Value:
Five
Three
One
Four
Two 
Using LinkedHashMap:
Complete Map content : {One=One, Two=Two, Three=Three, Four=Four, Five=Five}
Iterating Key-Value:
One
Two
Three
Four
Five
End of Main 
Output completed (0 sec consumed)

From  this example, we can clearly see that LinkedHashMap maintains key-value entries as it is inserted.