In this example we will see how and when to useJava.util.EnumMap.EnumMap is used when we need to have keys of the map asenums.

EnumMaps are represented internally asarrays. 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 mapmyMealMap.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 orderSystem.out.println(myMealMap.keySet());//We can get the value from enumTypeSystem.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 enumMapfor (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 enumMapfor (MealType mealType : myMealMap.keySet()) {if(MealType.SNACK.equals(mealType)){myMealMap.remove(MealType.SNACK);}}//map changed without throwing Concurrent modification ExceptionSystem.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 theenum keys were printed in the order they were input. We also saw how we can retrieve the values ofmap fromenum keys.

We also saw thatenumMap did not throwConcurrentModifactionExcpetion while trying to modify the map.

Download the Eclipse project of this tutorial:

So, in this example we saw how to useenumMap in Java.

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