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About Anirudh Bhatnagar

Anirudh Bhatnagar
Anirudh is a Java programmer with extensive experience in building Java/J2EE applications. He has always been fascinated by the new technologies and emerging trends in software development. He has been involved in propagating these changes and new technologies in his projects. He is an avid blogger and agile enthusiast who believes in writing clean and well tested code.

Java.util.EnumMap Example

In this example we will see how and when to use Java.util.EnumMap. EnumMap is used when we need to have keys of the map as enums.

EnumMaps are represented internally as arrays. This representation is extremely compact and efficient. Enummaps are maintained in the natural order of their keys (the order in which the enum constants are declared).

Lets see how to use them :
 
 
 

JavaEnumMapExample.java

package com.jcg.example;

import java.util.EnumMap;
import java.util.Map;

/**
 * 
 * @author anirudh
 *
 */
public class JavaEnumMapExample {
	
	public enum MealType{
		BREAKFAST,LUNCH,SNACK,DINNER
	}

	public static void main(String[] args) {
		
		Map myMealMap = new EnumMap(MealType.class);
                
                //populate the map
		myMealMap.put(MealType.BREAKFAST,"Enjoy Milk and Eggs for breakfast!");
		myMealMap.put(MealType.LUNCH,"Enjoy Chicken, Rice and bread for Lunch!");
		myMealMap.put(MealType.SNACK,"How about an apple for the evening snack!");
		myMealMap.put(MealType.DINNER,"Keep the dinner light, lets have some salad!");
		
		System.out.println("Welcome to meal planner, we have suggestions for following meals : ");
		
		//print all the keys of enum map in sorted order
		System.out.println(myMealMap.keySet());
		
		//We can get the value from enumType
		System.out.println(" Q: What should I have for lunch? ");
		System.out.println(" A: "+myMealMap.get(MealType.LUNCH));
		
		System.out.println(" Q: What should I have for snack? ");
		System.out.println(" A: "+myMealMap.get(MealType.SNACK));
		
		System.out.println(" Q: What should I have for dinner? ");
		System.out.println(" A: "+myMealMap.get(MealType.DINNER));

		//Iterate over enumMap
		for (MealType mealType : myMealMap.keySet()) {
			System.out.println(myMealMap.get(mealType));
		}
		System.out.println("*** Checking for concurrent modification exception! ***");
		//Does not throw Concurrent modification Exception in enumMap
		for (MealType mealType : myMealMap.keySet()) {
			if(MealType.SNACK.equals(mealType)){
				myMealMap.remove(MealType.SNACK);
			}
		}
		
		//map changed without throwing Concurrent modification Exception
		System.out.println(myMealMap);		
		
		
	}

}

Output:


Welcome to meal planner, we have suggestions for following meals : 
[BREAKFAST, LUNCH, SNACK, DINNER]
 Q: What should I have for lunch? 
 A: Enjoy Chicken, Rice and bread for Lunch!
 Q: What should I have for snack? 
 A: How about an apple for the evening snack!
 Q: What should I have for dinner? 
 A: Keep the dinner light, lets have some salad!
Enjoy Milk and Eggs for breakfast!
Enjoy Chicken, Rice and bread for Lunch!
How about an apple for the evening snack!
Keep the dinner light, lets have some salad!
*** Checking for concurrent modification exception! ***
{BREAKFAST=Enjoy Milk and Eggs for breakfast!, LUNCH=Enjoy Chicken, Rice and bread for Lunch!, DINNER=Keep the dinner light, lets have some salad!}

In the example we saw that the enum keys were printed in the order they were input. We also saw how we can retrieve the values of map from enum keys.

We also saw that enumMap did not throw ConcurrentModifactionExcpetion while trying to modify the map.

Download the Eclipse project of this tutorial:

So, in this example we saw how to use enumMap in Java.

Download
You can download the full source code of this example here: JavaEnumMapExample.zip
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