CODEWITHSUNDEEP
javaexception
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Reputation: 341

Return a value AND throw an exception?

I'm working with an API that claims to return true if it succeeds, and false if it fails. But, it also claims to throw different exceptions if it fails. How can it return false and throw an exception?

Upvotes: 31

Views: 61302

Answers (5)

Emmaline261
Emmaline261

Reputation: 11

Actually, you could throw an exception AND return a value (well, maybe not return but assign a value to a class variable) if you use try/catch/finally block.

public class ExceptionThrowingClass { public String valueToBeAssigned;

public void throwingExceptionMethod() throws Exception {
    try {
        //blah blah some code
        throw new Exception("this is the first exception");
    } catch (Exception ex){
         //rethrow the exception
        throw new Exception("this is the second exception", ex.getCause());
    } finally {
        valueToBeAssigned = "lets assign a value to a variable";
    }
}

}

However, it is not exactly a clean (or pretty) code so I'd avoid such solutions and just tried working with the exception itself (we have them to use them and not to misuse them).

Upvotes: 1

BenGee23
BenGee23

Reputation: 53

Although this question is old, I found a library that does so. It is to note that this uncommon and might be misleading to add values to the error object. This library wraps that behavior under the hood so you don't need to do it yourself and cause confusion for others working on your code: https://github.com/bacloud23/eager_return_js

It is in JavaScript but the same implementation can be done in Java.

Upvotes: 0

HesNotTheStig
HesNotTheStig

Reputation: 568

While it is possible to write your code in such a way that an exception AND a value can be derived from a function call (see the above posts), it should NEVER be done in proper coding.

I would love to a see a link to the documentation on this API. API's should place a priority on clarity. Throwing an exception and returning a value leaves the question of whether the value that was returned is safe to use or if it is invalid.

Remember, try/catch blocks are the OTHER method of handling exceptions. They don't pass the exception to the calling method, but handle it internally in a way that the developer deems appropriate.

If, for debugging purposes, you need to see the resulting value in the case of an exception, then Bohemian's idea works well.

Upvotes: 0

Bohemian
Bohemian

Reputation: 424983

You can throw an exception that has a (in this case boolean) value:

public class ValueException extends Exception {
    final boolean value;

    public ValueException(boolean value, String message) {
        super(message);
        this.value = value;
    }

    public boolean getValue() {
        return value;   
    }
}

Upvotes: 27

Jeremy Banks - Vive le Canada
Jeremy Banks - Vive le Canada

Reputation: 129735

It's not possible to both throw an exception and return a value from a single function call.

Perhaps it does something like returning false if there's an error, but throwing an exception if the input is invalid.

edit: PaulPRO posted a (now-deleted) answer pointing out that it is technically possible to cause an exception to be thrown in a different thread, while returning a value in the current one. I thought this was worth noting, even if it's not something you should ever see.

Upvotes: 31

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