Java Graph code explanation

Question

Hi all,
im new to java and have some trouble drawing a graph i looked up some code but dont quite understand it
can someone explain the following code please. I understand swing and painting and basic java.
Q1) Can please explain the flow of execution ?
Q2)
What i would also specifically like to understand about the code
is how does the graph keep going and looks like it scrolls across and not off the frame and how can i add this to a frame i already have
without covering over my other objects i have displayed.
Any help would be greatly appreciated.
Thanks
import java.awt.*;*
*import javax.swing.*;
import java.awt.event.*;*
*import javax.swing.event.*;
import java.awt.image.BufferedImage;
import java.awt.geom.*;*
*import java.math.*;
import java.util.*;*
*public class ecg extends JFrame*
*     myView view = new myView();*
*     Vector vr   = new Vector();*
*     int    ho   = 0;*
*public ecg()* 
*     addWindowListener(new WindowAdapter()*
    *{     public void windowClosing(WindowEvent ev)*
*          {     dispose();*
*               System.exit(0);}});*
*     for (int i=0; i < 5000; i++)*
*          int p = (int)(Math.random()*  260);
          vr.add(new Point(0,p-130));
     setBounds(3,10,625,350);
     view.setBounds(10,10,600,300);
     getContentPane().add(view);
     getContentPane().setLayout(null);
     setVisible(true);
     while (ho < 500-300)
          try
               Thread.sleep(110);
               ho = ho  +1;+
+               repaint();+
+          } catch (InterruptedException e) {}+
+     }+
+}+
+public class myView extends JPanel+
+{+
+     BufferedImage I;+
+     Graphics2D    G;+
+public myView()+
+{+ 
+}+
+public void paint(Graphics g)+
+{+
+     if (I == null)+
+     {+
+          I = new BufferedImage(getWidth(),getHeight(),BufferedImage.TYPE_INT_ARGB);+
+          G = I.createGraphics();+
+     }+
+     G.setColor(Color.white);+
+     G.fillRect(0,0,getWidth(),getHeight());+
+     G.setColor(Color.gray);+
+     Point p1,p2;+
+     p1 = (Point)vr.get(ho);+
+     int x = 0;+
+     for (int y=1; y < 600; y++)
          p2 = (Point)vr.get(y+ho);
          G.drawLine(x,p1.y+150,x+6,p2.y+150);
          p1 = (Point)vr.get(y+ho);
          x = x + 6;
     g.drawImage(I,0,0,null);
public static void main (String[] args) 
     new ecg();
}

Answer 1

Compiling your posted code gives a compiler warning:
C:\jexp>javac ecg.java
Note: ecg.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.
C:\jexp>javac -Xlint:unchecked ecg.java
ecg.java:31: warning: [unchecked] unchecked call to add(E) as a member of the raw type jav
a.util.Vector
            vr.add(new Point(0,p-130));
                  ^
1 warningWe can eliminate this by changing this
    Vector vr   = new Vector();to this
    Vector<Point> vr   = new Vector<Point>();The best way to understand things like this is to start a new file and slowly build it up so you can see what's going on, step-by-step. I've put in some comments and print statements to give you a start.
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
import javax.swing.event.*;
import java.awt.image.BufferedImage;
import java.awt.geom.*;
import java.math.*;
import java.util.*;
public class ECG extends JFrame
    myView view = new myView();
    Vector<Point> vr = new Vector<Point>();
    int    ho   = 0;
    public ECG()
        addWindowListener(new WindowAdapter()
            @Override
            public void windowClosing(WindowEvent ev)
                dispose();
                System.exit(0);
        // Initialize data in Vector.
        for (int i=0; i < 5000; i++)
            int p = (int)(Math.random() * 260); // range: (0    - 260]
            vr.add(new Point(0, p-130));        // range: (-130 - 130]
        System.out.println("Total number of data points: " + vr.size());
        setBounds(3,10,625,350);
        // Component drawing space is 600 wide by 300 high.
        view.setBounds(10,10,600,300);
        getContentPane().add(view);
        getContentPane().setLayout(null);
        setVisible(true);
        // Animate up thru the first 200 of 5000 data points.
        int millisPerSecond = 1000;
        long delay = 110;
        long framesPerSecond = millisPerSecond/delay;
        System.out.printf("Frames per second: %d%n", framesPerSecond);
        int paintSteps = 600;
        int dataIndex = 200;
                        //5000 -1 - paintSteps;  // max possible index
        System.out.printf("Expected animation time: %f seconds%n",
                           (double)dataIndex/framesPerSecond);
        long start = System.currentTimeMillis();
        // Animation loop.
        while (ho < dataIndex)
            try
                Thread.sleep(delay);
                // Increment "ho" which will step us through the Vector data.
                // Each new value draws the Vector graph data starting at
                // index "ho" placed at the left edge of the image/component.
                ho = ho + 1;
                long end = System.currentTimeMillis();
                double elapsedTime = (double)(end - start)/millisPerSecond;
                if(ho % 100 == 0)
                    System.out.printf("ho: %d  time: %.2f%n", ho, elapsedTime);
                // Update the image in the paint method.
                repaint();
            } catch (InterruptedException e) {
                System.out.println("animation interrupted");
        long end = System.currentTimeMillis();
        double elapsedTime = (double)(end - start)/millisPerSecond;
        System.out.printf("Total animation loop time: %f%n", elapsedTime);
    public class myView extends JPanel
        BufferedImage I;
        Graphics2D    G;
        public void paint(Graphics g)
            if (I == null)  // initializw image
                I = new BufferedImage(getWidth(),getHeight(),
                                      BufferedImage.TYPE_INT_ARGB);
                G = I.createGraphics();
            // Update image to show current state of animating graph.
            // Fill Background color.
            G.setColor(Color.white);
            G.fillRect(0,0,getWidth(),getHeight());
            // Set graph line color.
            G.setColor(Color.gray);
            // Draw next data segment to newly-erased image.
            // Get two points in data to draw the next line.
            Point p1,p2;
            // "ho" is a simple counter with range [0 - n-1]
            // [0 - 200-1] in the animation loop above.
            // Get the next data point at "ho" which will be drawn at
            // the beginning, ie, left edge (x = 0), of the image.
            p1 = vr.get(ho);
            int x = 0;
            // Since each frame starts at zero_x relative to the image:
            // x = 0.
            // Draw all graph data for this one 600 by 300 image frame
            // with data beginning at index "ho".
            for (int y=1; y < 600; y++)
                // Get the next point out ahead.
                p2 = vr.get(y+ho);
                // Draw a line from the last point, p1, to the next point, p2,
                // which will be spaced (x +=) 6 apart along the image/component
                // width of 600 (setBounds). Translate the y values down onto
                // the component by 150 pixels (the range of y values from
                // above is from -129 to 130). The "+150" shifts the y values
                // to the approximate center of the component.
                G.drawLine(x, p1.y+150, x+6, p2.y+150);
                // Save the current point to/in p1 for the next iteration.
                p1 = vr.get(y+ho);
                // Move along to the right in the image.
                x = x + 6;
            // Draw image in component.
            g.drawImage(I,0,0,null);
    public static void main (String[] args)
        new ECG();
}