defining "+" operator for new datatype

TexasDex · 04-02-2004, 10:22 AM

I am learning to program in JAVA and to teach myself class creation I have made the uConvert class, which has several sub-classes Length, Time, and Mass.

I want to be able to add different length objects

Code:

Length yourHeight = new Length();
Length myHeight = new Length();
myHeight.define(163,"cm");
yourHeight.define(68,"in");
Length ourHeight;

so that I can add them like:

Code:

ourHeight = myHeight + yourHeight;

instead of having to use this somewhat awkward method

Code:

ourHeight = myHeight.plus(yourHeight);

It works, but it is not "slick" or programmer-friendly

I have searched JAVA books, googled it to death, asked my Comp Sci instructor, to no avail. It always gives me this error:
"+" operator is not defined for Length,Length

I am using the Java SDK 1.3.1_09 on Windows XP, 2K and Redhat 8 machines, and nothing works.

rose_bud4201 · 04-02-2004, 11:22 AM

Sorry, there's no way to overload operators in Java like there is in C++. The java developers hard-coded the operators, and anything else has to be done like you're doing it, now.

TexasDex · 04-02-2004, 03:00 PM

That sucks

Why on earth wouldn't they let you do that? Is there some specific reason for it?

Well thanks anyway.

Komakino · 04-02-2004, 03:18 PM

Look up JFront on google. It's a java library that allows operator overloading. I've not tried it, but the example given looks easy enough.

rose_bud4201 · 04-02-2004, 05:25 PM

They did do that on purpose, yes. http://forum.java.sun.com/thread.jsp...rt=0&trange=15

kooch · 04-02-2004, 07:18 PM

really how tough of a concept is operator overloading?

not to sound haughty but some people just shouldn't program....

LFM vs. LFSP

Komakino · 04-03-2004, 05:57 AM

Quote:

Originally posted by kooch
really how tough of a concept is operator overloading?

not to sound haughty but some people just shouldn't program....

LFM vs. LFSP

I don't see the relevance... no one here is saying operator overloading is a difficult concept, only querying why something that useful isn't included in Java.

TexasDex · 04-03-2004, 10:39 AM

the relevance is that the JAVA designers thought that operator overloading was too difficult a concept for "the masses", and therefore left it out.

From what I can see, JFront is just a macro that "fixes" source code to change the code statements from the "a + b" syntax to the "a.operatorplus(b);" syntax. I'll look at it, but I really want my class to be reusable by other programmers (even if I never finish it) with the + operator. From what I've heard there is minor movement in the JAVA designers to include op. overloading but I'm not holding my breath.

BTW, when (if) I get the uConvert class and all it's sub-classes finished I hope to be able to multiply different types of units so that you can multiply different types of units and get different types of units
e.g.
Length * Length = Area
Area * Length = Volume

It would work something like this:

Code:

Length tracklength = new Length();
track.define(.25,"mi");

Time race1t = new Time();
Time.define(11.548,"sec");

Velocity myspeed = new Velocity();

// myspeed = tracklength / race1t  // doesn't work!  Damnit
myspeed = tracklength.div(race1t);

myspeed.outputType = 3; // type 3 = Miles/Hr
System.out.println(myspeed);

If I wanted to I could get really detailed and include stuff like Pascals, Joules, and even Moles.

Has anyone here done something like that, creating a comprehensive set of measurement datatypes? I will still continue to work on it if somebody already has, because this is primarily for my own education but it would be cool to contribute it to the community. BTW it will be under the GPL if I do bother to finish/release it.