Need some advide on drawing arrows.

Question

basically my program is almost done. I can have the use click on anywhere on the canvas and a filled circle pops up...can draw many circles at once.
i also manage to have the user have a choice to link them up circle to circle.
the problem comes when i try and draw arrow heads to the lines. The lines are connected from the centre of each circle to another centre of another circle..
so when the arrow heads appear, they will point in the right direction....but then the arrow head are blocked by the filled circles color..so i can't see them... how do i make the arrows point on the circles circumference?

Answer 1

I left the circles unfilled so you can see where the lines terminate and left the code in paintComponent; don't know how you are refactoring things. The lines could easily be added to another ArrayList.
import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import java.util.ArrayList;
import java.util.List;
import javax.swing.*;
public class DrawingTest
    public static void main(String[] args)
        CirclesAndArrows circles = new CirclesAndArrows();
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.getContentPane().add(circles.connector.getUIPanel(), "North");
        f.getContentPane().add(circles);
        f.setSize(400,400);
        f.setLocation(200,200);
        f.setVisible(true);
class CirclesAndArrows extends JPanel
    List circleList;
    final double DIA;
    boolean showLines;
    Connector connector;
    public CirclesAndArrows()
        circleList = new ArrayList();
        DIA = 20;
        showLines = false;
        setBackground(Color.white);
        connector = new Connector(this);
        addMouseListener(connector);
    protected void paintComponent(Graphics g)
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D)g;
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                            RenderingHints.VALUE_ANTIALIAS_ON);
        for(int j = 0; j < circleList.size(); j++)
            g2.draw((Shape)circleList.get(j));
        if(showLines)
            Ellipse2D.Double e1, e2;
            double x1, y1, x2, y2, phi;
            for(int j = 0; j < circleList.size(); j++)
                e1 = (Ellipse2D.Double)circleList.get(j);
                for(int k = j + 1; k < circleList.size(); k++)
                    e2 = (Ellipse2D.Double)circleList.get(k);
                    phi = Math.atan2(e2.y - e1.y, e2.x - e1.x);
                    x1 = e1.x + DIA/2 + (Math.cos(phi) * DIA + 1)/2;
                    y1 = e1.y + DIA/2 + (Math.sin(phi) * DIA + 1)/2;
                    x2 = e2.x + DIA/2 - (Math.cos(phi) * DIA - 1)/2;
                    y2 = e2.y + DIA/2 - (Math.sin(phi) * DIA - 1)/2;
                    g2.draw(new Line2D.Double(x1, y1, x2, y2));
    public void setCircle(Point p)
        Ellipse2D.Double e = new Ellipse2D.Double(p.x - DIA/2, p.y - DIA/2, DIA, DIA);
        circleList.add(e);
        repaint();
    public void setShowLines(boolean show)
        showLines = show;
        repaint();
    public void clear()
        circleList.clear();
        repaint();
class Connector extends MouseAdapter
    CirclesAndArrows circles;
    public Connector(CirclesAndArrows caa)
        circles = caa;
    public void mousePressed(MouseEvent e)
        circles.setCircle(e.getPoint());
    public JPanel getUIPanel()
        JButton clear = new JButton("clear");
        clear.addActionListener(new ActionListener()
            public void actionPerformed(ActionEvent e)
                circles.clear();
        final JCheckBox connect = new JCheckBox("connect circles");
        connect.addActionListener(new ActionListener()
            public void actionPerformed(ActionEvent e)
                circles.setShowLines(connect.isSelected());
        JPanel panel = new JPanel();
        panel.add(clear);
        panel.add(connect);
        return panel;
}