Re: Constrained ada type in Java

From: Brad BARCLAY (bbarclay_at_jsyncmanager.org)
Date: 12/11/03 

Date: Thu, 11 Dec 2003 04:10:41 GMT

Ed Trubia wrote:
> Have the following type that applies contraints. How could this be easily
> coded in Java

        There isn't really an elegant way of handling such things in Java as
you can in Ada.

        For type constraining, you'll probably want to create a class which
manages these constraints. Thus, if you want an integer type that can
only hold the ranges -45..150 (say, for storing temperature data),
create a class to hold it and ensure that the value it holds doesn't
exceed on underceed that range. For example:

        public class TemperatureData {
           private int temp = 0;

           public TemperatureData(int t) throws OutOfBoundsException {
              setTemp(t);
           }

           public setTemp(int t) throws OutOfBoundsException {
              if (t<-45 || t>150) throw new OutOfBoundsException;
              else temp=t;
           }

           public getTemp() {
              return temp;
           }
        }

        (Note that you'd have to also define OutOfBoundsException, as it
doesn't already exist).

        To handle method-level constraints, you'll have to test each variable
you want to constrain at the beginning of the method call, and then
throw an exception if it's out-of-bounds. The setTemp() method above
does just this.

        As I said, there isn't any nice way to do this like there is in Ada. I
was never completely sold on Ada, but this is one of the things I miss
(along with being able to call functions with your parameters in
whatever order you want to provide them in).

Brad BARCLAY 

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Relevant Pages

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