How to get enum value from property

问题

I have an enum with values VALID and INVALID, which have a boolean property associated with them. I would like to get the enum value based on a boolean value I provide.

If it is true I should get VALID, if it is false I should get INVALID. I would like to do so in a getter method like the below, based on the value of the member variable

public boolean getCardValidityStatus() {
    return CardValidationStatus status = CardValidationStatus(this.mCardValidityStatus));
}

My code:

private enum CardValidationStatus {
    VALID(true),
    INVALID(false);

    private boolean isValid;
    CardValidationStatus(boolean isValid) {
        this.isValid = isValid;
    }
    public boolean getValidityStatus() {
        return this.isValid;
    }
}

回答1:

You're able to achieve that using a static lookup method in the enum itself:

private enum CardValidationStatus {
    VALID(true),
    INVALID(false);

    //...

    public static CardValidationStatus forBoolean(boolean status) {

        //this is simplistic given that it's a boolean-based lookup
        //but it can get complex, such as using a loop...
        return status ? VALID : INVALID; 
    }
}

And the appropriate status can be retrieved using:

public CardValidationStatus getCardValidityStatus() {
    return CardValidationStatus.forBoolean(this.mCardValidityStatus));
}

回答2:

I would add a parse method to your enum, which takes the boolean, iterates over all the values and returns the one that matches, for example:

public CardValidationStatus parse(boolean isValid) {
    for (CardValidationStatus cardValidationStatus : CardValidationStatus.values()) {
        if (cardValidationStatus.getValidityStatus() == isValid) {
            return cardValidationStatus;
        }
    }

    throw new IllegalArgumentException();
}

回答3:

@ernest_k solution made this work, but I think that's not reliable solution.

You should always do code which is independent.

Because his solution is hardcoded. What if values of VALID & INVALID are changed. Will you change your forBoolean logics also?
Because he did not check what the Enum fields are holding inside it.

Reliable solution will be @DaveyDaveDave answer. This will also work when you have many status with VALID & INVAlID.

private enum CardValidationStatus {
    VALID(true),
    INVALID(false);

    //...

    public CardValidationStatus forBoolean(boolean isValid) {
        for (CardValidationStatus cardValidationStatus : CardValidationStatus.values()) {
            if (cardValidationStatus.getValidityStatus() == isValid) {
                return cardValidationStatus;
            }
        }

        throw new IllegalArgumentException();
    }
}

Suggestion (Easiest way I think)

Why are you making Enum just for storing 2 boolean values?

Just make static boolean named by VALID & INVALID.

public static final boolean CARD_STATUS_VALID = true;
public static final boolean CARD_STATUS_INVALID = false;

if(cardStatus == CARD_STATUS_VALID){
 // todo
}

来源：https://stackoverflow.com/questions/52004191/how-to-get-enum-value-from-property

标签

java

enumeration