Two dimensional array list

You would use

List<List<String>> listOfLists = new ArrayList<List<String>>();

And then when you needed to add a new “row”, you’d add the list:

listOfLists.add(new ArrayList<String>());

I’ve used this mostly when I wanted to hold references to several lists of Point in a GUI so I could draw multiple curves. It works well.

For example:

import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.RenderingHints;
import java.awt.Stroke;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.util.ArrayList;
import java.util.List;
import javax.swing.*;

public class DrawStuff extends JPanel {
   private static final int PREF_W = 400;
   private static final int PREF_H = PREF_W;
   private static final Color POINTS_COLOR =;
   private static final Color CURRENT_POINTS_COLOR =;
   private static final Stroke STROKE = new BasicStroke(4f);
   private List<List<Point>> pointsList = new ArrayList<List<Point>>();
   private List<Point> currentPointList = null;

   public DrawStuff() {
      MyMouseAdapter myMouseAdapter = new MyMouseAdapter();

   public Dimension getPreferredSize() {
      return new Dimension(PREF_W, PREF_H);

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