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).