Question
I know that double behaves differently than Double but I don't yet know all of the details. For example for:
protected double[] _refPoint = new double[3];
public void setReferencePoint(double[] point){
_refPoint = point;
}
Does this do a shallow copy or a deep copy?
Answer
No copy at all, it just changes the _refPoint variable to reference the passed in array, and presumably eventually garbage collects the old double[3]. This is not in general a good idea, because the code may not behave the way the caller expects, for example:
double d = { 1, 2, 3}
setReferencePoint(d);
d[0] = 3;
changes the array which is now referenced internally by the class containing setReferencePoint. It is probably better practice to internally clone the array, or to make sure the documentation to setReferencePoint explains that it will hold a reference to the array and the user should not modify it.
In fact we generally discourage the use of double[3] for momentum or space point. Try using Hep3Vector instead:
http://java.freehep.org/freehep-physics/apidocs/hep/physics/vec/Hep3Vector.html