Appending to arrays of arrays

Processing Coding Questions
9

Well, here is one example. You have an unknown number of layers, and each layer is full of an unknown number of points, and each point contains 2 or 3 floats (2D or 3D). It should be easy to add layers and points, and get them.

ArrayList<ArrayList<PVector>> layers;

Okay, initialize your layers – a list of (lists of (points)).

layers = new ArrayList<ArrayList<PVector>>();

and add a layer – which is a list of points:

layers.add(new ArrayList<PVector>());

now get layer 0

ArrayList<PVector> layer0 = layers.get(0);

and add some points to layer 0

layer0.add(new PVector(0, 0));
layer0.add(new PVector(50, 50));
layer0.add(new PVector(random(0, width), random(0, height)));

now retrieve layer 0, point 1 from your layers object:

PVector pt = layers.get(0).get(1);

and draw its x, y:

ellipse(pt.x, pt.y, 20, 20);

The example:

ArrayList<ArrayList<PVector>> layers;
layers = new ArrayList<ArrayList<PVector>>();
layers.add(new ArrayList<PVector>());
ArrayList<PVector> layer0 = layers.get(0);
layer0.add(new PVector(0, 0));
layer0.add(new PVector(50, 50));
layer0.add(new PVector(random(0, width), random(0, height)));
PVector pt = layers.get(0).get(1);
ellipse(pt.x, pt.y, 20, 20);
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