Making a little library

[Saiqal]

Hello everybody 
I'm trying to make myself a little collection of classes that are custom to my needs. I started making a couple like Vector and Point. The problem is I want to be able to use any data type that I want, double,  float, int etc. but I want to make one class that can do any of them. the problem would be the getters and setters as I would have to define what type I will return. Also I don't want to allocate memory for things that I won't be using in the instance of the class as it's pretty much useless. So my question is is there a dynamic way to get around this problem without something like the code below ?

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class Point{   int nx,ny;   double dx,dy;   Point(int x, int y){     this.nx = x;     this.ny = y   }   Point(double x, double y){     this.dx = x;     this.dy = y   } }

Thank you in advance

[StrideColossus]

If your class is immutable then you could parameterise it using a generic type along these lines:

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public class Point<T extends Number> {    private T x, y;        public Point( T x, T y ) {       this.x = x;       this.y = y;    } }

However this will quickly break down if you need your class to do anything vaguely useful such as addition (e.g. try using a += operator in that class!)

Check out the Point2D classes in the java.awt.geom package which does something similar.

[matheus23]

I'm trying to make myself a little collection of classes that are custom to my needs. I started making a couple like Vector and Point. The problem is I want to be able to use any data type that I want, double,  float, int etc. but I want to make one class that can do any of them.

Haha, not in java

Here is a scala example of how to create a generic Vec2:
http://matheusdev.tumblr.com/post/51071594017/scala-and-extending-numeric-t
And don't worry, It's the same performance as if you'd write a Vec2 for each numeric type (that is: byte, char, short, int, float and double, or only float and double if you decide to use Fractional).

Yeah, it's not trivial, but it's possible in scala

In java: No... not really. Try to find a code precompiler for java maybe, but in the end that's what scala is.

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[Saiqal]

Man that's a shame. I will have to make int and double version of everything 
Thank you for your replies though. You illuminated me 

[Riven]

I think multiple vector types are overrated. I never needed anything else than floats and ints for vectors.

[tyeeeee1]

Man that's a shame. I will have to make int and double version of everything 
Thank you for your replies though. You illuminated me 

It shouldn't be too tough to make a method for all of them. Just type one up and then CnP and adjust for each. =P

[Saiqal]

It's not tough as coding goes. But it certainly is more elegant if I could do what I originally wanted to do. I'll have to live with it thought 

[quew8]

Other alternative is to write the class in c(++) where this is trivial then jni it it. But if you're going to go to this much trouble then you might as well use scala.

[actual]

With Java, it's essentially cut and paste code, or using code generation with templates the way most primitive collection libraries do it.

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public class Point<T extends Number> {    private T x, y;        public Point( T x, T y ) {       this.x = x;       this.y = y;    } }

Isn't another problem with the generics approach is that now you are dealing with Float, Integer, and Double rather than their primitive counterparts?

Not to side track the discussion, but I have toyed with the idea of separate semantically meaningful vector classes (such as units of measure). Ideally you would get a compile time error if you tried to add a Velocity to an Acceleration or something like that.

I haven't thought of a way to do it in Java that reads nicely and has good performance, and isn't a hassle. Phantom types get you a part of the way there but type erasure is a pain. Scala's value classes looks to be a nice approach.

[sproingie]

If you write the class in scala, you may want to add the @specialized annotation to the type parameter, which basically creates instances for primitive types.

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class Vec2[@specialized T](val x: T, val y: T)(implicit num: Fractional[T]) {   // ... etc }

Truth is, I don't know how compatible it is with typeclasses though, and I don't have scala on this box, so try it out?

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[ags1]

Just write a little more code and save yourself the hassle of unexpected bugs and incompatibilities.

[wessles]

If your class is immutable then you could parameterise it using a generic type along these lines:

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public class Point<T extends Number> {    private T x, y;        public Point( T x, T y ) {       this.x = x;       this.y = y;    } }

However this will quickly break down if you need your class to do anything vaguely useful such as addition (e.g. try using a += operator in that class!)

Check out the Point2D classes in the java.awt.geom package which does something similar.

Thanks! I had almost given up on what those carrots meant in java! Then I just randomly find this!