Question

I have a codebase that deals with angles quite a bit, but sometimes the input comes in different angle formats. That is, some formats are degrees clockwise, some are degrees counter-clockwise, some are 0 to 360, some are -180 to 180, some are radians…

So far I have succeeded in keeping them all the same internally, but it’s always a worry, and the bugs that arise can be hard to track down.

I would like to create an angle class that keeps track of the units and direction as well as the magnitude so that I can deal with them in a uniform way without so much worries.

My googling has turned up Martin Fowler’s Value Object, but i’m having trouble understanding his language without a simple example to reference. I’ve also found a Java API that seems relevant, but it doesn’t look like a simple example either…

Can anyone point me towards a simple example of a class that incorporates units?

Answer 1

I would approach this by storing values internally in a single format (say, positive radians) and provide static factory methods to construct angles from various input formats. For example:

public class Angle {
  private final double radians;

  private Angle(double radians) {
    this.radians = radians;
  }

  // Static factory methods

  public static Angle radians(double rad) {
    return new Angle(rad);
  }

  public static Angle degrees(double deg) {
    return radians(Math.toRadians(deg));
  }

  public static Angle degreesCCW(double deg) {
    return degrees(360 - deg);
  }

  ...

  // Operations

  public Angle plus(Angle other) {
    return new Angle((this.radians + other.radians) % (2 * Math.PI));
  }

  ...
}

Then you could use it like this:

Angle a1 = Angle.radians(0.5);
Angle a2 = Angle.degreesCCW(60);
Angle a3 = a1.plus(a2);