Re: Call by Result

From:

Cholo Lennon <chololennon@hotmail.com>

Newsgroups:

comp.lang.java.programmer

Date:

Thu, 16 Jun 2011 11:30:22 -0300

Message-ID:

<itd41d$pjf$1@speranza.aioe.org>

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