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, for example:
public void setReferencePoint(double[] point){ _refPoint = point.clone(); }
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