Looping over multiple objects in Java

Context

I am trying to loop over multiple dataseries in the following code from this repo:

// configuring everything by default
Plot plot = Plot.plot(null).
    // setting data for data series one
    series("dataseries One", Plot.data().
        xy(1, 2).
        xy(3, 4), null);
    // setting data for data series two
    series("dataseries Two", Plot.data().
        xy(10, 20).
        xy(30, 40), null);

// saving sample_minimal.png
plot.save("sample_minimal", "png");

However, the number of dataseries (two arraylist of List<Double> x and List<Double> y objects), is currently hardcoded and I am experiencing some difficulties looping through an arbitrary amount of dataseries/lines.

In particular I thought I could write a for loop like:

for(int i = 0; i < y_data_series; i++){
    series(f'Data Series {i}', Plot.data().
                                xy(x_data_series.get(i),y_data_series.get(i)),

But the dot at the end of Plot plot = Plot.plot(null). implies a series method is expected instead of a for loop.

Question

How could I loop over the two arraylists of dataseries within the Plot object?

Doubts

0. I think my question is a bit ill-posed because I do not yet exactly know how the syntax works, when a series method is "called" on another series method with a dot in between. I hope the context however clarifies what the question is.
1. I would think a zip/map/fold might be an option as they might be functions just like the series method.

I am not exactly sure on whether I understand your question, but I think something along these lines should work for you:

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
public class PlotTest {
public static void main(String[] args) {
Plot plot = Plot.plot(null);
final List<List<Double>> multipleXseries = new ArrayList<List<Double>>();
final List<List<Double>> multipleYseries = new ArrayList<List<Double>>();
final List<Double> xSeries1 = new ArrayList<Double>();
final List<Double> ySeries1 = new ArrayList<Double>();
xSeries1.add(0D);ySeries1.add(10D);
xSeries1.add(1D);ySeries1.add(20D);
xSeries1.add(2D);ySeries1.add(30D);
multipleXseries.add(xSeries1);
multipleYseries.add(ySeries1);
final List<Double> xSeries2 = new ArrayList<Double>();
final List<Double> ySeries2 = new ArrayList<Double>();
xSeries2.add(0D);ySeries2.add(15D);
xSeries2.add(1D);ySeries2.add(25D);
xSeries2.add(2D);ySeries2.add(35D);
multipleXseries.add(xSeries2);
multipleYseries.add(ySeries2);
for(int i = 0; i < multipleXseries.size(); i++) {
Plot.Data data = Plot.data().xy(multipleXseries.get(i), multipleYseries.get(i));
plot = plot.series("Data Series " + i, data, null);
}
try {
plot.save("test", "png");
} catch (IOException e) {
e.printStackTrace();
}
}
}