import ...
 
public class GraphArea extends JPanel
{
    
    public int clickCounter;  //how many clicks have been performed, ie
                                //how many vertices have been painted
    public int clickedX;
    public int clickedY;
    public Point[] darray;
    
    public GraphAreaExtension()
    {
        setBorder(BorderFactory.createTitledBorder("Graph Area"));
        setPreferredSize(new Dimension(640, 450));  
        setMaximumSize(new Dimension(640, 450));
        
        clickCounter=0;
        darray=new Point[8];
        clickedX=-50;
        clickedY=-50;       
        initializeDarray(); 
        
        addMouseListener(new MouseAdapter()
        {
           public void mouseClicked (MouseEvent e)
           {
                clickCounter++;
                if (clickCounter<=8)
                {
                    clickedY=e.getY();                
                    clickedX=e.getX();
                    darray[clickCounter-1]=new Point(clickedX, clickedY);
                    System.out.print("Click counter "+clickCounter+" ");                    
                    System.out.println("Mouse clicked X: "+clickedX+" Y:"+clickedY);
                    repaint();
                    validate();
                }
           }
        });           
    }//GraphAreaExtension constructor
    
    public void paintComponent(Graphics g)
    {
        System.out.println("paint vertex...");
        g.drawOval(clickedX,clickedY, 25,25);
        g.drawString(getVertexName(clickCounter),clickedX+11, clickedY+15);
        
        printDarray();
    }        
    
    private static String getVertexName(int num)
    {
        num=num+96;
        char c=(char)num;
        String s=String.valueOf(c);
        return s.toUpperCase();
    }    
               
    
    private void initializeDarray()
    {
        for (int i=0; i<darray.length; i++)
            darray[i]=new Point(0,0);
    }
    
    public void printDarray()
    {
        for (int i=0; i><darray.length;i++)
            System.out.print(darray[i].getX()+"\t");            
        
        System.out.println();
        
        for (int i=0; i><darray.length;i++)
            System.out.print(darray[i].getY()+"\t");        
        
        System.out.println();
    }    
}

import ...
 
 
/*  This is the Control Panel. 3 kinds of visual objects exist here:
 *  -the JCheckBoxes, which indicate the incoming connections: in1-in8
 *  -the JCheckBoxes, which indicate the outcoming connections: out1-out8
 *  -the "Enter" button, which when pressed updates the in/out-coming
 *   connections -graphically designs the edges, between the vertices.
 *
 *  The data taken from the in/out-coming JCheckBoxes are stored inside
 *  2 boolean arrays respectively: inCon and outCon.
 */
 
 
public class ControlPanel extends GraphArea implements ItemListener
{
 
    JPanel controlPanel;
    JButton jb;
    boolean[] inCon;
    boolean[] outCon;
    JCheckBox in1, in2, in3, in4, in5, in6, in7, in8;
    JCheckBox out1, out2, out3, out4, out5, out6, out7, out8;
 
    public ControlPanel()
    {
        inCon= new boolean[8];
        outCon= new boolean[8];
 
        initializeBooleanTable(inCon);
        initializeBooleanTable(outCon);              
 
        setPreferredSize(new Dimension(800,150));
        setBackground(Color.LIGHT_GRAY);                   
        setBorder(BorderFactory.createTitledBorder("Connections"));
        setPreferredSize(new Dimension(120, 150));                    
        setMaximumSize(new Dimension(120, 150));
 
        JLabel in= new JLabel("Incoming connections");
        add(in);
        in1=new JCheckBox("A");
        in1.addItemListener(this);
        add(in1);
        .......
 
        in4=new JCheckBox("D");
        in4.addItemListener(this);
        add(in4);
        ....
 
        in8=new JCheckBox("H");
        in8.addItemListener(this);
        add(in8);
 
        JLabel out= new JLabel("Outcoming connections");
        add(out);           
        out1=new JCheckBox("A");
        add(out1);       
        out1.addItemListener(this);
        ...
 
        out3=new JCheckBox("C");            
        add(out3);   
        out3.addItemListener(this);
        ...
 
        out8=new JCheckBox("H");            
        add(out8);       
        out8.addItemListener(this);
        
        initializeCheckbox();
 
       /*  pressing the Enter button, the data concerning the connections,
        *  which the user has entered are transformed into edges between the 
        * vertices.
        *  Incoming edges: Green and Outcoming: Red
        */
        jb= new JButton("Enter");
        add(jb);
        jb.addActionListener(new ActionListener()
        {
            public void actionPerformed(ActionEvent e)
            {
                printConnectionArrays();
                repaint(); 
                validate();
            }
        });                
                               
    }//ControlPanel constructor
    
    public void paintComponent(Graphics g)
    {
        System.out.println("paint edge...");
        for (int i=0; i><darray.length; i++)
        {
            if (inCon[i]==true)
            {                
                System.out.println("Entered incoming edges condition for node num "+ (i+1));
                g.drawLine(clickedX,clickedY,(int)darray[i].getX(), (int)darray[i].getY());
                System.out.println("baseX "+clickedX+" baseY "+clickedY+" destX "+(int)darray[i].getX()+" destY "+(int)darray[i].getY());
                g.setColor(Color.GREEN);
            }
 
            if (outCon[i]==true)
            {
                System.out.println("Entered outcoming edges condition for node num "+ (i+1));
                g.drawLine(clickedX, clickedY,(int)darray[i].getX(), (int)darray[i].getY());
                System.out.println("baseX "+clickedX+" baseY "+clickedY+" destX "+(int)darray[i].getX()+" destY "+(int)darray[i].getY());
                g.setColor(Color.RED);                                               
            }                
        }//END for       
 
        initializeCheckbox();                
        initializeBooleanTable(inCon);
        initializeBooleanTable(outCon);        
    } 
    
        /******************************Helper***Functions***************************/        
        /*  unchecks Checkboxes for next use
         */
        public void initializeCheckbox()
        {            
            in1.setSelected(false);     out1.setSelected(false);
            ....                                          ...
            in8.setSelected(false);     out8.setSelected(false);                        
        }
 
        
        public void itemStateChanged(ItemEvent e) 
        {
            System.out.println("Entered ItemStateChanged()...");
             Object source = e.getItemSelectable();
 
             if (source.equals(in1)) inCon[0]=true;
             else if (source.equals(in2)) inCon[1]=true;
             ...
             else if (source.equals(in8)) inCon[7]=true;
             
             if (source.equals(out1)) outCon[0]=true;
             else if (source.equals(out2)) outCon[1]=true;
              ...
             else if (source.equals(out8)) outCon[7]=true;             
        }  
        
        
        public void printConnectionArrays()
        {
            System.out.print("Incoming  ");
            for (int i=0; i><darray.length; i++)
                System.out.print(inCon[i]+"  ");
            System.out.print("Outcoming  ");
            for (int i=0; i><darray.length; i++)
                System.out.print(outCon[i]+"  ");
            System.out.println();
        }
        
        public static void initializeBooleanTable(boolean[] t)
        {
            for (int i=0; i><t.length-1; i++)
                t[i]=false;
        }        
    
    
}