deep copy / clone a object

Programming Questions

clankill3r

in Programming Questions • 1 year ago

I got a class called BezierVertexPath that holds:

private PApplet p;
private BezierMethods bezierMethods = BezierMethods.getInstance();
// It's set to private so the user can't access the control points
// private BezierVertex start;
private ArrayList<BezierVertex> bezierVertexes = new ArrayList<BezierVertex>();
protected float l; // length of the total path
// when a bezierVertex get's added or a position get's changed it get's
// dirty
private boolean dirty = true;
// extra one for the arc length parameterization
private boolean dirtyALP = true;
protected boolean dirtyWeight = true;
// arc length parameterization on/off
protected boolean alp = false;
// stores length, points and tangents for faster return
private boolean ALPStore = false;
private ALP_info ALP_info;
// stepAccuracy is used for bezierMethods
private float stepAccuracy = 0.85f;
private boolean lockControls = true;
// stores at what value t is found (for closestBezierPoint for example)
protected float targetT;
// when true the end will be connected to the start
private boolean close = false;

ALP_info is a inner class of BezierVertexPath that holds:

float l;
float[] bezierLengths;
PVector[] bezierPoints;
PVector[] bezierTangents;

And BezierVertex (holded in the ArrayList in the BezierVertexPath class) contains a few objects simulair PVector (but called CVector).

I want to be able to make a copy/clone of BezierVertexPath. However, all deeper fields/objects should be copied as well.

There are multiple ways to do and i have no experience with it.

What i dislike about a constructor like this:

BezierVertexPath(BezierVertexPath original) {
// code
}

Is that i'm afraid to forget to add new fields that i might add in the future which might lead to hard to fix bugs.

I can't really figure out the difference between a deep copy and a clone, is it only the way how it get's created?

And what would be easier in my case judging from the fields given above?

Hope someone can help, internet is confusing the hell out of me :)

Replies(7)

quarks

Re: deep copy / clone a object

1 year ago

I can't really figure out the difference between a deep copy and a clone, is it only the way how it get's created?

You are not really comparing like with like when duplicating objects there are two things to consider

the type of copy (shallow or deep)
the copy method to use (copy constructor or clone)

You appear to be aware of the difference between shallow and deep copying and you have stated

However, all deeper fields/objects should be copied as well.

so a deep copy is required.

The decision is then which copy method to use. The advantage of the copy constructor is simple syntax but then you have to do all the shallow copying as well as the deep copying. The clone method has more complex syntax but then it will do the shallow copying part itself.

I would suggest that you use the copy constructor because the syntax is easier to get right. I know you said

Is that i'm afraid to forget to add new fields that i might add in the future which might lead to hard to fix bugs.

but you will just have to remember

clankill3r

Re: deep copy / clone a object

1 year ago

ok, copy constructor it will be then

clankill3r

Re: deep copy / clone a object

1 year ago

are there cases that the copy constructor doesn't work (or get insane complex)?

I have a class BezierVertexPath.

This hols a ArrayList with BezierVertex

BezierVertex has:

protected BezierVertex next;
protected BezierVertex previous;

Let's go back to BezierVertexPath,

let's say i want to make a copy of the ArrayList that holds the BezierVertexes:

public BezierVertexPath(BezierVertexPath original) {
ArrayList<BezierVertex> bezierVertexes = new ArrayList<BezierVertex>();
for(BezierVertex bv : original.bezierVertexes) {
BezierVertex copy = BezierVertex(bv);
}
}

this will have next and previous wrong.

Do i run into simulair problems with a clone method?

The other things are easier to solve.

calsign

Re: deep copy / clone a object

1 year ago

You can use ArrayList's constructor that takes a List (or an ArrayList, as this is a descendant of List):

ArrayList<BezierVertex> bezierVertexes = new ArrayList<BezierVertex>(original.bezierVertexes);

PhiLho

Re: deep copy / clone a object

1 year ago

calsign, the elements of the two array lists will be shared, that's no a deep copy.

clankill3r, your code fragment isn't even correct (or complete), on syntax and logic...

You can do something like:

public BezierVertexPath(BezierVertexPath original) {
// Initialize the class field
bezierVertexes = new ArrayList<BezierVertex>(original.size());
for (BezierVertex bv : original.bezierVertexes) {
BezierVertex copy = new BezierVertex(bv); // This need to be a copy constructor of the BezierVertex class, copying the fields of this class
bezierVertexes.add(copy);
}
}

To do a deep copy of a complex object, you should have ways to do deep copy of each object present as field of this class, by means of copy constructors or other means.

clankill3r

Re: deep copy / clone a object

1 year ago

that takes not care of the field next and previous.

I think i have to make the copy constructor for BezierVertex protected.

and then something like

for(int i = 0; i < bezierVertexes.size()-1; i++) {

BezierVertex current = bezierVertexes.get(i);

BezierVertex next = bezierVertexes.get(i+1);

current.next = next;

}

+ previous handling.

will give it another attempt later.

PhiLho

Re: deep copy / clone a object

1 year ago

" that takes not care of the field next and previous."
Yes, that's what I wrote in my comment: " This need to be a copy constructor of the BezierVertex class, copying the fields of this class"

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