How to match and switch Strings against enums?

Question

I want to transform a String into an enum. But how?

class Letter {
    A, B, C
}

String letter = "A";
switch (letter) {
    case Letter.A: //cannot convert from Letter to String
    case Letter.A.toString(): //case expressions must be constant expressions
    case Letter.C.name(): //case expressions must be constant expressions
    default:
}

http://stackoverflow.com/questions/604424/java-convert-string-to-enum is this what you want? — X-Pippes, Oct 24 '13 at 13:21

score 5 · Accepted Answer · answered Oct 24 '13 at 13:21

5

First the Letter must be an enum:

enum Letter {
    A, B, C
}

Letter letter = Letter.valueOf("A")
// and just switch
switch (letter) {
    case A:
    case B:
    case C:
}

answered Oct 24 '13 at 13:21

René Link

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Sergey Kalinichenko · Answer 2 · 2013-10-24T13:29:34.267

3

You can do it like this:

String letter = "A";
switch (Letter.valueOf(letter)) {
    case A: // No problem!
    case B:
    case C:
    default:
}

Demo on ideone.

edited Oct 24 '13 at 13:29

answered Oct 24 '13 at 13:22

Sergey Kalinichenko

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This will not work I guess. – shikjohari Oct 24 '13 at 13:24
2

We can't use qualified name of enum constants in cases. They have to be unqualified names. So that should be `case A:`. – shikjohari Oct 24 '13 at 13:26

score 2 · Answer 3 · answered Oct 24 '13 at 13:24

Make that enum first instead of Class Replace to this

Letter obj = Letter.valueOf(letter);
switch (obj) {
    case A: //cannot convert from Letter to String
    case B: //case expressions must be constant expressions
    case C: //case expressions must be constant expressions
    default:

Prabhakaran Ramaswamy · Answer 4 · 2013-10-24T13:28:03.160

1

Do like this.

Letter l = Letter.valueOf("A");

or

Letter l = Enum.valueOf(Letter.class, "A");

switch (l) {
    case A:
    case B:
    case C:
    default:
}

edited Oct 24 '13 at 13:28

answered Oct 24 '13 at 13:22

Prabhakaran Ramaswamy

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Paul Vargas · Answer 5 · 2013-10-24T13:34:12.190

1

If the string don't match with some constant in the enum, throws an java.lang.IllegalArgumentException: No enum constant. Try with the next:

class Letter {
    A, B, C;
    public static Letter fromString(String str) {
    if (str != null) {
      for (Letter l : Letter.values()) {
        if (l.toString().equals(str)) {
            return l;
        }
      }
    }
    return null;
  }
}

edited Oct 24 '13 at 13:34

answered Oct 24 '13 at 13:28

Paul Vargas

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How to match and switch Strings against enums?

5 Answers5