Draw points defined in file in Java

Question

I am trying to learn some of the graphics side of Java. I made a text file that lists the points and the first line in the file determines how many points there are. I need to take the points in the text file and plot them on a canvas. I have looked at several resources and I just do not understand how everything works together. I cannot even find a tutorial that gives all of the code and explains where each part goes and how it is called. Basically, I am confused by JPanels, JFrames, and basically the whole process. Below is the code that I have written so far and a screen shot of what the file looks like.

Code:

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
import java.awt.Graphics.*;
import java.util.*;
import java.io.*;

public class drawPoints extends JPanel
{

public void paintComponent(Graphics g)
{
super.paintComponent(g);
this.setBackground(Color.WHITE);
g.setColor(Color.BLUE);



  try{

  FileInputStream fstream = new FileInputStream("Desktop/Assign2Test1.txt");


  DataInputStream in = new DataInputStream(fstream);
  BufferedReader br = new BufferedReader(new InputStreamReader(in));
  String strLine;

 int i = 1;
  while ((strLine = br.readLine()) != null){

  final Point[] points = new Point[Integer.parseInt(br.readLine())];

  final String[] split = strLine.split("\u0009"); 
  points[i++] = new Point(Integer.parseInt(split[0]), Integer.parseInt(split[1])); 

  }

  in.close();
    }catch (Exception e){  System.err.println("Error: " + e.getMessage());
  }


}




import javax.swing.*;

public class mainDrawPoint
{
public static void main(String args[])
  {

  JFrame f = new JFrame("Draw Points Application");
  f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  drawPoints dP = new drawPoints();
  f.add(dP);
  f.setSize(500,500);
  f.setVisible(true);
  }
}

All the code is doing is putting the values in an array.

The x and y coordinates are separated by a tab. Any help would be appreciated!

Answer 1

Something you should consider is the following:

From what I can tell, the first number in there is the count. If that is indeed it, you don't need the LinkedList for the Strings. Build a Point array, for example:

final Point[] points = new Point[Integer.parseInt(br.readLine())];

From there, using that looping system you have with the strLine variable, use that String and work out how to parse it, for example:

int i = 0; // Put this outside of the while loop. 
//While loop condition check here

final String[] split = strLine.split("\u0009"); // Unicode character for tab. 
points[i++] = new Point(Integer.parseInt(split[0]), Integer.parseInt(split[1])); // Assuming length 2 of split.

As for rendering the points, create a new class, one that extends JPanel. In that class, add the following code and fill in the TODO:

@Override
public void paintComponent(final Graphics g){
    //TODO: Paint what you want here, automatically double-buffered
}

Now, when you create a new Panel class and add it to a JFrame, whenever you call for a repaint() from the JFrame it will render the code in the paintComponent() method of the Panel class. If you have any other questions, feel free to ask.

Edit: Example code:

import javax.swing.*;
import java.awt.*;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;

public class Test {

    private static final String FILE = "Desktop/Assign2Test1.txt";
    private static Point[] points;

    public static void main(final String[] args){
        try{
            final BufferedReader br = new BufferedReader(new FileReader(new File(FILE)));
            points = new Point[Integer.parseInt(br.readLine())];
            int i = 0;
            int xMax = 0;
            int yMax = 0;
            while(br.ready()){
                final String[] split = br.readLine().split("\u0009");
                final int x = Integer.parseInt(split[0]);
                final int y = Integer.parseInt(split[1]);
                xMax = Math.max(x, xMax);
                yMax = Math.max(y, yMax);
                points[i++] = new Point(x, y);
            }
            final JFrame frame = new JFrame("Point Data Rendering");
            final Panel panel = new Panel();
            panel.setPreferredSize(new Dimension(xMax + 10, yMax + 10));
            frame.setContentPane(panel);
            frame.pack();
            frame.setVisible(true);
            frame.repaint();
        } catch (final Exception e){
            e.printStackTrace();
        }
    }

    public static class Panel extends JPanel {

        @Override
        public void paintComponent(final Graphics g){
            g.setColor(Color.RED);
            for(final Point p : points){
                g.fillRect((int) p.getX(), (int) p.getY(), 2, 2);
            }
        }

    }

}

Answer 2

obtain the instance of the Graphics object from the element by using the panel.getGraphics() method. later use the graphics object to draw lines using the graphics.drawLine() method.

you can split the content of a line using a regex string.split("\t"). this will give you an array with 2 elements (since you say that each line contains 2 numbers with a tab in between).