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From: Cholo Lennon <chololennon@hotmail.com>
Newsgroups: comp.lang.java.programmer
Subject: Re: Call by Result
Date: Thu, 16 Jun 2011 11:30:22 -0300
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On 10/06/2011 03:03, Gene Wirchenko wrote:
> Dear Java'ers:
>
>       I wish to call by result with a method.  Is it possible?  If not,
> can it be easily simulated in an unnasty way?
>
>       I am writing a simple preprocessor.  I have a few spots where a
> string needs to be parsed.  I want to call something like this:
>            String ReturnString="";
>            boolean DidItWork=GetString(ReturnString);
>            if (!DidItWork)
>               // too bad
> It is not acceptable to have a special String value mean failure.  I
> want the method to be able to return any potential string.
>
> Sincerely,
>
> Gene Wirchenko

IMHO using exceptions is not always the best answer to this problem (as 
other suggested).

How about using a simple generic class? (of course, it could be 
corrected or improved. A similar idea could be found in other languages 
(such as C++ (boost)):

class Optional<T> {
     private T value;
     private boolean valid;

     public Optional(T value) {
         setValue(value);
     }

     public Optional() {
         this.valid = false;
     }

     public boolean isValid() {
         return this.valid;
     }

     public T getValue() {
         return this.value;
     }

     public void setValue(T value) {
         this.value = value;
         // TODO Shall I set to true when value is null?
         this.valid = true;
     }

     public void invalidate() {
         this.value = null;
         this.valid = false;
     }
}

// Test
Optional<String> result = GetString();
if (!result.isValid()) {
    // too bad
    ...
}
else {
    System.out.print(result.getValue());
    ...
}


Regards


-- 
Cholo Lennon
Bs.As.
ARG