Using enum as key for map

Question

I want to use enum as keys and a object as value. Here is the sample code snippet:

public class DistributorAuditSection implements Comparable<DistributorAuditSection>{      

     private Map questionComponentsMap;  

     public Map getQuestionComponentsMap(){  
         return questionComponentsMap;  
     }  

     public void setQuestionComponentsMap(Integer key, Object questionComponents){  
         if((questionComponentsMap == null)  || (questionComponentsMap != null && questionComponentsMap.isEmpty())){ 
             this.questionComponentsMap = new HashMap<Integer,Object>();  
         }  
         this.questionComponentsMap.put(key,questionComponents);  
     }
}

It is now a normal hashmap with integer keys and and object as values. Now I want to change it to Enummap. So that I can use the enum keys. I also don't know how to retrieve the value using Enummap.

What have you tried? What happens when you use `EnumMap`? To get help you need to be more specific and show you've done your homework. — Sean Owen, Oct 01 '12 at 08:06

score 53 · Answer 1 · edited Sep 06 '18 at 12:22

53

It the same principle as Map Just Declare enum and use it as Key to EnumMap.

public enum Color {
    RED, YELLOW, GREEN
}

Map<Color, String> enumMap = new EnumMap<Color, String>(Color.class);
enumMap.put(Color.RED, "red");
String value = enumMap.get(Color.RED);

You can find more about Enums here

edited Sep 06 '18 at 12:22

Nicolas Filotto

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answered Oct 01 '12 at 08:10

Amit Deshpande

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1

Thx. I was missing the Colors.RED concept for declaring a constant: i.e. private static final Colors R = Colors.RED; – Ross Youngblood Jan 27 '17 at 15:45
why we have added Color.class in map argument ?? – Keshav Oct 14 '20 at 06:36

score 9 · Answer 2 · answered Oct 01 '12 at 08:13

9

Just replace new HashMap<Integer, Object>() with new EnumMap<MyEnum, Object>(MyEnum.class).

answered Oct 01 '12 at 08:13

Puce

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public void setQuestionComponentsMap(Integer key, Object questionComponents){ what can i pass in the place of "Integer key"?coz now i am retrving enum keys. – user1568579 Oct 01 '12 at 10:13
If you can change the signature of that method then just replace the Integer argument with your Enum type... – Puce Oct 01 '12 at 10:48

Using enum as key for map

2 Answers2

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