CODEWITHSUNDEEP
javainheritanceenums
Benny
Benny

Reputation: 93

enum inheritance, or something similar

I have a string (which is a message) that I get as input and I need to do one of 4 possible things depending on the string I know that there is eunm.valueOf() option, but I have 4 different enums, each with few possible messages.

looks something like: 

public enum first{ONE,TWO,THREE};
public enum second{FOUR,FIVE,SIX};
public enum third{SEVEN,EIGHT,NINE};

public void work(String message){
    //Here I want to compare message string to one of the 3 enums
}

is it possible to do this in one method of the enum? or should I just try to create one, and if I get an exception try the other and so on?

Upvotes: 7

Views: 9898

Answers (6)

Péter Török
Péter Török

Reputation: 116266

As others have commented, it may be better to think through whether you really need 4 distinct enums.

But if you do, you could have them implement a common interface. Then you can map the input strings to the appropriate enum member, and call its method to accomplish what you want. Something like

public interface SomeInterface {
  void doSomething();
};

public enum First implements SomeInterface {
  ONE,TWO,THREE;
  @Override
  public void doSomething() { ... }
};
...
Map<String, SomeInterface> myMap = new HashMap<String, SomeInterface>();
for (First item : First.values()) {
  myMap.put(item.toString(), item);
}
...

public void work(String message){
  SomeInterface obj = myMap.get(message);
  if (obj != null) {
    obj.doSomething();
  }
}

This assumes that the 4 possible things you want to do correspond to the 4 enums. If not, you can override the method separately for each and any enum member too, e.g.

public enum First implements SomeInterface {
  ONE,
  TWO {
    @Override
    public void doSomething() { // do something specific to TWO }
  },
  THREE;
  @Override
  public void doSomething() { // general solution for all values of First }
};

Upvotes: 6

Bob Cross
Bob Cross

Reputation: 22292

What you're really looking for is a aggregation of the other enums. The easiest way to get that is to make a new enum that puts all of those choices in a new enum. Something to this effect:

public enum Combination {
    NEWONE(first.ONE), NEWTWO(first.TWO), NEWTHREE(first.THREE),
    NEWFOUR(second.FOUR), NEWFIVE(second.FIVE), NEWSIX(second.SIX),
    NEWSEVEN(third.SEVEN), NEWEIGHT(third.EIGHT), NEWNINE(third.NINE);

    private String contents;

    public Combination(first f) {
        contents = f.toString();
    }

    public Combination(second s) {
        contents = s.toString();
    }

    public Combination(third t) {
        contents = t.toString();
    }

    public String toString() {
        return contents;
    }
}

This will more correctly aggregate the previous enums into a single data structure.

Upvotes: 1

Peter Lawrey
Peter Lawrey

Reputation: 533492

You can create a Map of them all

 static final Map<String, Enum> enumMap = new LinkedHashMap<String, Enum>(){{
     for(First e: First.values()) put(e.name(), e);
     for(Second e: Second.values()) put(e.name(), e);
     for(Third e: Third.values()) put(e.name(), e);
 }};

 Enum e = enumMap.get(name);

Upvotes: 1

Mark Tozzi
Mark Tozzi

Reputation: 10903

Even given your odd/even example in the comments, I don't feel multiple enums are the way to go here. I would use something like (warning, untested):

public enum Numbers {
ONE("first"), TWO("first"), THREE("first"), FOUR("second"), FIVE("second"), SIX("second"), SEVEN("third"), EIGHT("third"), NINE("third")

private String type;

Numbers(String t) { this.type = t; }
String getType { return this.type; }
}

Then you can use valueOf() to look up the enum element, and getType() to find out which of your three categories it belongs to.

Upvotes: 0

Avi
Avi

Reputation: 20142

It isn't entirely clear what you are asking, but perhaps you want to define a mapping between strings and constants, like this:

enum Type { FIRST, SECOND, THIRD };
Map<String, Type> mapping = new HashSet<String, Type>(){{
    put("ONE", Type.FIRST);
    put("TWO", Type.FIRST);
    //...
    put("NINE", Type.THIRD);
}};

public Type getTypeFromString(String s) {
    return mapping.get(s);
}

Upvotes: -1

pickypg
pickypg

Reputation: 22332

Enumerations in Java are full blown classes. Individual values can even override the behavior to meet their needs. It's pretty cool. You can use this to your advantage:

public enum Value implements Worker
{
    ONE,
    TWO,
    THREE
    {
        @Override
        public void doWork(String message)
        {
            // overrides behavior of base enum
        }
    },
    FOUR,
    /* ... */,
    NINE;

    private final String message;

    Value() { this(""); }
    Value(String message) { this.message = message; }

    public void doWork(String message)
    {
        if (this.message.equals(message))
        {
            /* ... */
        }
    }
}

public interface Worker
{
    void doWork(String message);
}

Upvotes: 1

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