How to match Enum Objects with their associated constant values?

Question

I created this enum:

public enum CoffeeSorts {
    Coffee("Kaffee"), Espresso("Espresso"), Mocca("Mocca"), Cappuccino(
            "Cappuccino"), LatteMacchiato("Latte Macchiato"), DoubleEspresso(
            "doppelter Espresso");

    private final String stringValue;

    private CoffeeSorts(final String s) {
        stringValue = s;
    }

    public String toString() {
        return stringValue;
    }
}

I tried the following way to use it

public ACoffee createCoffee(String type) {

        switch (type) {
        case CoffeeSorts.Cappuccino :
            try {
                return new ChocolateSprincles(new Cream(new Coffee()));
            } catch (Exception e) {}
            return null;
            break;
        case CoffeeSorts.LatteMacchiato :
            try {
                return new ...
            }
        .
        .
        .
    }

It only gives me an Error saying "cannot convert from CoffeeSorts to String". Can you tell me what i did wrong?

can you be more specific? Maybe provide a stacktrace? – Savv Jun 10 '14 at 10:41 — Savv, Jun 10 '14 at 10:41
Compiler should be referenced as "it", not "He". – Infinite Recursion Jun 10 '14 at 10:46 — Infinite Recursion, Jun 10 '14 at 10:46

score 5 · Accepted Answer · answered Jun 10 '14 at 10:42

Your type variable is a String, but you're trying to specify values which are CoffeeSort values. You'll need to convert the String to a CoffeeSort first, or change the signature.

For example:

public ACoffee createCoffee(CoffeeSort type) {
    ...
}

or

public ACoffee createCoffee(String typeName) {
    CoffeeSort type = CoffeeSort.valueOf(typeName);
    ...
}

Also note that you can't break; after a return statement, as it's unreachable code. (I hope your exception handling isn't really like that, either...)

Finally, consider changing your code entirely to put a createCoffee method inside the enum itself. Then you won't need a switch statement at all. You can make it an abstract method which is overridden in each enum value.

public enum CoffeeSort {
    Coffee("Kaffee") {
        @Override public ACoffee createCoffee() {
           ...
        }
    },
    Espresso("Espresso") { ... },
    Mocca("Mocca") { ... },
    Cappuccino("Cappuccino") { ... },
    LatteMacchiato("Latte Macchiato") { ... },
    DoubleEspresso("doppelter Espresso") { ... };

    private final String stringValue;

    private CoffeeSorts(final String s) {
        stringValue = s;
    }

    @Override
    public String toString() {
        return stringValue;
    }

    public abstract ACoffee createCoffee();
}

I like most of your post, but that pattern you're proposing with the factory methods inside the enum values is really not my cup of tea ;-) — Robby Cornelissen, Jun 10 '14 at 10:56
@RobbyCornelissen: Coffee/tea differences, aside, it depends on the context. I *love* putting behaviour inside enums when it really belongs there - when it's not context-specific, for example. Is the `CoffeeSort` type the piece of code which should unambiguously know how to create a cup of coffee? If so, my solution is great IMO - polymorphism wins over switch/case where feasible. If, however, you've got different situations (e.g. "create a cup of coffee in XML form" vs "create a cup of coffee as JSON") then it's a different matter. — Jon Skeet, Jun 10 '14 at 11:00

score 4 · Answer 2 · answered Jun 10 '14 at 10:42

4

The type in your switch(type) should be an object of type CoffeeSorts. You're passing in a string.

answered Jun 10 '14 at 10:42

Robby Cornelissen

91,784
22
134
156

score 2 · Answer 3 · edited May 23 '17 at 12:05

2

Your method signature should be:

public ACoffee createCoffee(CoffeeSorts type)

Your switch statement works on type and the case statements that you put there only make sense if type is of type CoffeeSorts.

Sidenote: enums are typically capitalized in Java (see Coding Conventions - Naming Enums).

edited May 23 '17 at 12:05

Community

1
1

answered Jun 10 '14 at 10:41

reto

9,995
5
53
52

How to match Enum Objects with their associated constant values?

3 Answers3