enum type with numeric constant

Question

I'm getting data from a legacy system where a certain one byte field is a code that may contain a letter or a number. I want to map it to an enum but I'm not sure how to handle the numeric values.

public enum UsageCode {
    A ("Antique"),
    F ("Flood Damaged"),
    N ("New");
//  0 ("Unknown")  How to allow for value of "0"?

    private final String description;

    UsageCode(String description) {
        this.description = description;
    }

    public String getDescription() {
        return description;
    }
}

ENUMS should be used as constants and not as dynamic values. You should be better off using your own implementation. — Abhishek
– Abhishek, Commented Apr 21, 2011 at 16:06
@Abhishek, it is a good and perfectly valid practice to represent a known and finite range of (primitive) values with an enum. — Péter Török
– Péter Török, Commented Apr 21, 2011 at 16:10
@peter-torok I agree on finite ranges but he is trying to retrieve te values from a database so my assumption was the values are not known only the Range(A-Z & 0-9) is known. — Abhishek
– Abhishek, Commented Apr 21, 2011 at 16:15

Péter Török · Accepted Answer · 2011-04-21 16:16:08Z

7

Turn it inside out:

public enum UsageCode {
    ANTIQUE ('A'),
    FLOOD_DAMAGED ('F'),
    NEW ('N');
    UNKNOWN ('0')

    private static final Map<Character, UsageCode> charToEnum
            = new HashMap<Character, UsageCode>();

    static { // Initialize map from legacy code to enum constant
        for (UsageCode code : values())
        charToEnum.put(code.getCode(), code);
    }

    // Returns UsageCode for legacy character code, or null if code is invalid
    public static UsageCode fromLegacyCode(char code) {
        return charToEnum.get(code);
    }

    private final char code;

    UsageCode(char code) {
        this.code = code;
    }

    public char getCode() {
        return code;
    }
}

For converting the incoming character codes into enum values, I added an inner Map<Character, UsageCode> and a static conversion method.

Example adapted from Effective Java 2nd Edition, Item 30.

edited Apr 21, 2011 at 16:16

answered Apr 21, 2011 at 16:06

Péter Török

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2 Comments

Tom Over a year ago

Thanks for your help. I also need to be able to print a description for each value so I guess I could so something like: ANTIQUE ('A', "Antique") and update the constructor.

Péter Török Over a year ago

@Tom, indeed, you can freely add further properties (or even polymorphic behaviour) to your Java enum.

Community · Accepted Answer · 2012-05-30 08:35:50Z

5

You can do it other way round, having a meaningful constant and storing legacy value representation:

public enum UsageCode {

   ANTIQUE("A"),
   FLOOD_DAMAGED("F"),
   NEW("N"),
   UNKNOWN("0");

   private String legacy;

   private UsageCode(String legacy) {
      this.legacy = legacy;
   }

   public static UsageCode toUsageCode(String legacyOutput) {
      for(UsageCode code : values()) {
         if (code.legacy.equals(legacyOutput)) {
            return code;
         }
      }
      return null;
   }
}

edited May 30, 2012 at 8:35

CommunityBot

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answered Apr 21, 2011 at 16:07

mindas

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