Two dimensional array list

Question

I've heard of using a two dimensional array like this :

String[][] strArr; 

But is there any way of doing this with a list?

Maybe something like this?

ArrayList<String><String> strList; 

And using something like this to add to it?

strList.add("hey", "hey"); 

Any way of doing something like this? Any help appreciated.

It would be good if there is because i am currently putting strings into two differrent ArrayList's in pairs.

Answer 1

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.*;  @SuppressWarnings("serial") 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 = Color.red;    private static final Color CURRENT_POINTS_COLOR = Color.blue;    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();       addMouseListener(myMouseAdapter);       addMouseMotionListener(myMouseAdapter);    }     @Override    public Dimension getPreferredSize() {       return new Dimension(PREF_W, PREF_H);    }     @Override    protected void paintComponent(Graphics g) {       super.paintComponent(g);       Graphics2D g2 = (Graphics2D) g;       g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,              RenderingHints.VALUE_ANTIALIAS_ON);       g2.setStroke(STROKE);       g.setColor(POINTS_COLOR);       for (List<Point> pointList : pointsList) {          if (pointList.size() > 1) {             Point p1 = pointList.get(0);             for (int i = 1; i < pointList.size(); i++) {                Point p2 = pointList.get(i);                int x1 = p1.x;                int y1 = p1.y;                int x2 = p2.x;                int y2 = p2.y;                g.drawLine(x1, y1, x2, y2);                p1 = p2;             }          }       }       g.setColor(CURRENT_POINTS_COLOR);       if (currentPointList != null && currentPointList.size() > 1) {          Point p1 = currentPointList.get(0);          for (int i = 1; i < currentPointList.size(); i++) {             Point p2 = currentPointList.get(i);             int x1 = p1.x;             int y1 = p1.y;             int x2 = p2.x;             int y2 = p2.y;             g.drawLine(x1, y1, x2, y2);             p1 = p2;          }       }    }     private class MyMouseAdapter extends MouseAdapter {       @Override       public void mousePressed(MouseEvent mEvt) {          currentPointList = new ArrayList<Point>();          currentPointList.add(mEvt.getPoint());          repaint();       }        @Override       public void mouseDragged(MouseEvent mEvt) {          currentPointList.add(mEvt.getPoint());          repaint();       }        @Override       public void mouseReleased(MouseEvent mEvt) {          currentPointList.add(mEvt.getPoint());          pointsList.add(currentPointList);          currentPointList = null;          repaint();       }    }     private static void createAndShowGui() {       JFrame frame = new JFrame("DrawStuff");       frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);       frame.getContentPane().add(new DrawStuff());       frame.pack();       frame.setLocationRelativeTo(null);       frame.setVisible(true);    }     public static void main(String[] args) {       SwingUtilities.invokeLater(new Runnable() {          public void run() {             createAndShowGui();          }       });    } } 

Answer 2

You can create a list,

ArrayList<String[]> outerArr = new ArrayList<String[]>();  

and add other lists to it like so:

String[] myString1= {"hey","hey","hey","hey"};   outerArr .add(myString1); String[] myString2= {"you","you","you","you"}; outerArr .add(myString2); 

Now you can use the double loop below to show everything inside all lists

for(int i=0;i<outerArr.size();i++){     String[] myString= new String[4];     myString=outerArr.get(i);    for(int j=0;j<myString.length;j++){       System.out.print(myString[j]);     }    System.out.print("\n");  }