Processing has a built in function for that: arrayCopy().

Don't copy the reference, but copy the object. In the case of PVector you should change the line to:

1. previousPoints[i] = currentPoints[i].get();

An arraylist where you constantly add a new coordinate and remove the oldest is perhaps even easier here.

Java does not support pointers that is a C/C++ thing. The eqivalent in Java is the reference.

1. PVector a, b, x;
2. x = new PVector();
3. a = x;
4. b = a;

If the above code variables a, b & x are 'object references' and at line 1 they will be initialised by Java to null. They are not PVector objects because we have not used the new command to create any yet.

In line 2 we create a new PVector object and Java will give this object a unique reference number which is then stored in the variable x

The crunch comes in line 2, it is copying the reference number from x into a. It means that both a and x reference the same object. Then in line three copies the reference number in a into b. Now all three object referneces refer to the same object. Using a, b or x to change the value in the PVector will change the same object.

Looking at your code and assuming that the object previousPoints has already been created then use this solution

1. previousPoints[i].set(currentPoints[i]);
2. currentPoints[i] = newly discovered pixel matching labled colour.

If it has not been created then

1. previousPoints[i] = new PVector();
2. previousPoints[i].set(currentPoints[i]);
3. currentPoints[i] = newly discovered pixel matching labled colour.

It is a shame that PVector does not have a copy constructor or cloneable so the first 2 lines could be done is a single statement.

HTH

Thank you all very much - I've never received so many straightforward answers to one problem so quickly. I'm still having difficulties in tracing pixels in an image but I'll start a new question for it rather than spiral this one into a different topic (I've spent 2 days trying to get somewhere).