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Thread: How to read from all files in a directory & plot the contents?

  1. #1
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    Feb 2010
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    Default How to read from all files in a directory & plot the contents?

    /*PS: This topic has something to do with Java graphics as well*/
    I'm working on a star map (graphics program), the final output of the program is similar to:

    These are the steps i follow:
    Step 1
    Write a method to convert between star coordinate system to the Java picture coordinate system.
    The star coordinate system has (0,0) in the center, and −1 and 1 as the extremes.
    The Java graphics coordinate system has (0,0) as the top-left corner, and positive numbers extend down and right up to the screen size.
    ---->diagram: http://i45.tinypic.com/2z4fgog.jpg

    Step 2
    Read the contents of the star-data.txt file, and plot the stars on a Java graphics window. Use a black background, and plot the stars as white circles.
    star-data.txt contains info on 3,526 stars, this number appears on the first line of the file.
    Subsequent lines has the following fields:
    -x, y coordinates for stars (in star coordinate system, e.g. 0.512379, 0.020508)
    - Henry Draper number (just a unique identifer for the star)
    -magnitude (or brightness of star)
    -names of some stars. A star may have several names.
    Step 3
    Vary the size of the circles to reflect their magnitude. Since brighter stars have smaller magnitude values, you will need to calculate the circle radius, say, 10/(magnitude + 2).

    Step 4
    Read from all files in constellation folder, and plot them on top of the stars.
    Each file contains pairs of star names that make up lines in the constellation.

    I have already done Steps 1 - 3.
    I'm using files :
    -StarApp.java as my application class that has main() method
    -StarJFrame.java ,this class creates the window & defines its properties & behavior
    -StarJPanel.java ---> heres the code, for this class, below
    -Star.java -----> heres the code, for this class, below

    import java.awt.*;
    import javax.swing.*;
    import java.awt.event.*;
    import java.util.Scanner;
    public class StarJPanel extends JPanel implements ActionListener {
    	private Star[] stars;
    	private Timer timer;
    	public StarJPanel() {
    		timer = new Timer(5, this);
    		stars = getArrayOfStars();
    	private Star[] getArrayOfStars() {
    		// This method reads the Stars data from a file and stores it in the stars array.
    		int howMany = Integer.parseInt(Keyboard.readInput());
    		Star[] stars = new Star[howMany];
    		for (int i = 0; i < stars.length; i++) {
    			String input = Keyboard.readInput();
    			Scanner fields = new Scanner(input);
    			double x = Double.parseDouble(fields.next());
    			double y = Double.parseDouble(fields.next());
    			int draper = Integer.parseInt(fields.next());
    			double magnitude = Double.parseDouble(fields.next());
    			String namesString = "";
    			String[] names = {};
    			if (fields.hasNext()) {
    				namesString = fields.nextLine();
    				names = namesString.trim().split("; ");
    			stars[i] = new Star(x, y, draper, magnitude, names);
    		return stars;
    	public void actionPerformed(ActionEvent e) {
    	public void paintComponent(Graphics g) {
    		for(int i = 0; i < stars.length; i++) {
    			stars[i].coordinateToPixel(stars[i].getX(), stars[i].getY());

    import java.awt.*;
    import javax.swing.*;
    public class Star {
    	private double x, y;		// coordinates of star
    	private int draper;			// Henry Draper number (unique identifier)
    	private double magnitude;	// Magnitude (brightness) of star
    	private String[] names;		// Star name(s) - not always present
    	private int newX;
    	private int newY;
    	private int size;
    	public Star( double x, double y, int draper, double magnitude, String[] names ) {
    		this.x = x;
    		this.y = y;
    		this.draper = draper;
    		this.magnitude = magnitude;
    		this.names = names;
    		size = (int)(10/(magnitude + 2));
    	public void coordinateToPixel(double x, double y) {
    		newX = (int) ( (x + 1) * 350);
    		newY = (int) ( (y - 1) * -350);
    	public void drawStar(Graphics g) {
    		g.drawOval( newX, newY, size, size);
    	public int getNumberOfNames() {
    		return names.length;
    	public double getX() {
    		return x;
    	public double getY() {
    		return y;

    As you can see I have done:
    Step 1: in Star class, with method: coordinateToPixel(double x, double y)
    Step 2: in StarJPanel class with method: private Star[] getArrayOfStars()
    (PS: I'm also using Keyboard class to read lines from the stars.txtfile)
    Step 3: in Star class, with method: drawStar(Graphics g), where size = (int)(10/(magnitude + 2));

    Please tell me if I have done 3 steps without confusing & incoherent code, I guess I have written the code differently from what ppl write. Somehow thats how we were taught to write. For me, my way gets a bit confusing sometimes!!

    Now I'm left stuck with Step 4.
    I have a folder where all my StarApp, StarJPanel, etc files are & a folder called Constellation
    Inside constellation folder I have files that contain pairs of star names that make up lines in the constellation.
    --Heres the constellation folder & star-data.txt file:
    Constellations & star-data.rar

    Although I'm thinkin i can use below code to read contents in files & use g.drawLine somewhere in StarJPanel. But I'm not sure how to find same names of stars in constellation files with names in the already set array from star-data & then join the coordinates with g.drawLine ???

    import java.io.*;
    public class reader {
    	public static void main(String args[]) throws Exception {
    		FileReader fr = new FileReader("Constellation/....");         /** Don't know what to put in ....... **/
    		BufferedReader br = new BufferedReader(fr);
    		String s;
    		while((s = br.readLine()) != null) {

    Not sure how Step 4 is done please guide me.
    By the way, I'm using textpad as my editor & complier.
    So I have to go: Tools > Run in parameters i put: StarApp < star-data.txt inorder to load the Stars into screen.
    Last edited by 123; February 10th, 2010 at 04:49 AM.

  2. #2
    Administrator copeg's Avatar
    Join Date
    Oct 2009
    Thanked 833 Times in 772 Posts
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    Default Re: How to read from all files in a directory & plot the contents?

    If you have a directory name, you can get a ref to every file in the directory by calling listFiles(), and from there read each file accordingly. You can consider setting up a Set or a HashMap of your stars based upon their name, then it is easy and fast to look them up by name and retrieve the coordinates to draw the constellations.

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