Not 100% sure what you are asking, but I'll give it a try. Assuming you have a list of Points...
List<Point2D> points = Arrays.asList(new Point2D.Double(12., 34.),
new Point2D.Double(56., 78.));
... you can turn that list into a 2D-array like this:
double[][] array = points.stream()
.map(p -> new double[] {p.getX(), p.getY()})
.toArray(double[][]::new);
... or into a nested list like this:
List<List<Double>> list = points.stream()
.map(p -> Arrays.asList(p.getX(), p.getY()))
.collect(Collectors.toList());
In both cases, the result looks like this [[12.0, 34.0], [56.0, 78.0]]
, as an array or a list, respectively.
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