Groovy And JScience Sunday, June 04, 2006

I have been spending a lot of time investigating Groovy lately. I wanted to dig in to writing a Groovy Category so I started writing some code to support things like this...

def duration = 30.minutes + 2.hours

Before I got too far along there I discovered that John Wilson had already implemented a lot of that in his TimeCategory which is part of Google Data Support.

I had recently read a JNB article that Lance Finney had written on JScience and that gave me another idea. I decided to write a Groovy Category that would use JScience to support things like this...

def len = 2.kilometers + 500.meters

Since I wanted to do this as an exercise I decided to not even do any research to find out if anyone had already implemented something like this. I wanted to build this for my own benefit as a learning exercise. I started by expressing some of my own requirements in the form of a Groovy Unit Test like this...

class JScienceTest extends GroovyTestCase {

  void testConversions() {
    use(JScienceCategory) {
      def len = 2.kilometers
      assertEquals 2.0,    len.kilometers,  0.00001
      assertEquals 2.0E3,  len.meters,      0.00001
      assertEquals 2.0E5,  len.centimeters, 0.00001
      assertEquals 2.0E6,  len.millimeters, 0.00001
      assertEquals 2.0E9,  len.micrometers, 0.00001
      assertEquals 2.0E12, len.nanometers,  0.00001
      
      def len2 = 400.centimeters
      assertEquals 4.0E-3, len2.kilometers,  0.00001
      assertEquals 4.0,    len2.meters,      0.00001
      assertEquals 4.0E2,  len2.centimeters, 0.00001
      assertEquals 4.0E3,  len2.millimeters, 0.00001
      assertEquals 4.0E6,  len2.micrometers, 0.00001
      assertEquals 4.0E9,  len2.nanometers,  0.00001
    }
  }
  
  void testAddition() {
    use(JScienceCategory) {
      def len = 2.kilometers + 500.meters
      assertEquals 2.5, len.kilometers, 0.00001
    }
  }
  
  void testSubtraction() {
    use(JScienceCategory) {
      def len = 3.kilometers - 500.meters
      assertEquals 2.5, len.kilometers, 0.00001
    }
  }
  
  void testMultiplication() {
    use(JScienceCategory) {
      def len = 3.kilometers * 2
      assertEquals 6.0, len.kilometers, 0.00001
    }
  }
  
  void testDivision() {
    use(JScienceCategory) {
      def len = 42.meters / 3
      assertEquals 14.0, len.meters, 0.00001
    }
  }
}

My Groovy Kung Fu is still developing and I had not done anything at all with JScience before this. Even with those limitations I was able to get all of those tests passing in about an an hour.

Would you rather do this in Java...

Measure length = Measure.valueOf(50, SI.CENTI(SI.METER)).plus(Measure.valueOf(25.0, SI.METER));
Measure lengthInCentimeters = length.to(SI.CENTI(SI.METER));
System.out.println("length in centimeters is " + lengthInCentimeters.getEstimatedValue());

Or do this in Groovy...

def length = 50.centimeters + 25.meters
println "length in centimeters is ${length.centimeters}"

Isn't Groovy fun? :)