Java: enum toString()

Question

I have created an enum and I'm trying to allow my enum to support a String.format operation that gets unlimited number of parameters are return a string. I only managed to return an object and after using this method I have to do a toString()/casting. I am guessing there's a more "clean" way to do it, or maybe to override better the toString() method. Basically, I wanted to support the toString() method but sadly didn't manage to do that so I created this method. As you can see it's named text(..) and not toString().

How can I do this better? The ideal solution I wanted was something like toString(..) which returns a String.

public enum MY_ENUM {

    VALUE_A("aaa %s"), VALUE_B("bbb %s");

    private String text;

    MY_ENUM(String text) {
        this.text = text;
    }

    public String text() {
        return this.text;
    }

    public Object text(final Object... o) {
        return new Object() {
            @Override
            public String toString() {
                return String.format(text(), o);
            }
        };
    }
}

Solution 1

I see where you're going... I think this is what you want (tested, and it works):

public String toString(Object... o) {
    return String.format(text, o);
}

For a design point of view, I would not publish the text (ie have the getter) unless you really need to - the fact that text is used as a format string is an implementation choice. I would simply do this:

public static enum MY_ENUM {

    VALUE_A("aaa %s bbb %s"),
    VALUE_B("bbb %s");

    private final String text;

    MY_ENUM(String text) {
        this.text = text;
    }

    public String toString(Object... o) {
        return String.format(text, o);
    }
}

As an aside, I really like the idea of the class. Haven't seen it before.

Solution 2

You can't override toString() if you need to pass more parameters (toString() doesn't receive any). Simply define a new method in the enum, no need to override:

public String getAsFormattedText(Object... o) {
    return String.format(text, o);
}

You shouldn't name this method toString(), it'd be confusing because you're not returning the string representation of the current object, instead you're returning a formatted string of the objects passed as parameters. Also, the text() method should be called getText(), that's the Java convention.

Better use a name that clearly indicates that the returned string is not any string - it's a formatted string that expects the text to be formatted as a parameter - getAsFormattedText() clearly expresses this.

Comments

[Popokoko]

Great solution, works perfectly, erm, i was really close to solve it myself, thanks a lot!

[mP.]

Yes very confusing when someone doesnt want to pass any params but gets the parameterless toString.

[thecoshman]

I like this idea too, though I would favour using a function more like anEnumValue.format(Object o). to me, 'toString' should return a string representation of the enum value itself, so VALUE_A would be like "aaa <object toString> bbb <objecttoString>".

[Bohemian]

@thecoshman that is true of toString() without a parameter ( ie overriding Object's impl), but toString() with parameter(s) can do what it likes. There are lots of examples from the JDK that use this pattern, for example Integer.toString(int).

[thecoshman]

@Bohemian fair point, though we are of course arguing semantics here now. I'd still favour .format(...) over .toString(...) in this context.