Drawing nonoverlapping n sided polygon , circles and ellipse with mouse on JPanel on buffrered image

Question

I want a Java swing program to draw non-overlapping n-sided polygon , circles and ellipse with the mouse.

The polygon should not add the last point and first point itself until user makes it.

Answer 1

This is a REALLY basic example

 public class DrawPolygon {

      public static void main(String[] args) {
           new DrawPolygon();
      }

      public DrawPolygon() {
           EventQueue.invokeLater(new Runnable() {
                @Override
                public void run() {
                     try {
                          UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                     } catch (ClassNotFoundException ex) {
                     } catch (InstantiationException ex) {
                     } catch (IllegalAccessException ex) {
                     } catch (UnsupportedLookAndFeelException ex) {
                     }

                     JFrame frame = new JFrame("Test");
                     frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                     frame.setLayout(new BorderLayout());
                     frame.add(new PolyPane());
                     frame.pack();
                     frame.setLocationRelativeTo(null);
                     frame.setVisible(true);
                }

           });
      }

      public static class PolyPane extends JPanel {

           private MouseHandler mouseHandler;
           private Path2D currentShape;
           private List<Path2D> lstPloys;
           private Point lastPoint;
           private Point currentPoint;

           public PolyPane() {
                lstPloys = new ArrayList<>();
           }

           @Override
           public Dimension getPreferredSize() {
                return new Dimension(200, 200);
           }

           @Override
           public void addNotify() {
                super.addNotify();
                addMouseListener(getMouseHandler());
                addMouseMotionListener(getMouseHandler());
           }

           @Override
           public void removeNotify() {
                removeMouseListener(getMouseHandler());
                removeMouseMotionListener(getMouseHandler());
                super.removeNotify();
           }

           public MouseHandler getMouseHandler() {
                if (mouseHandler == null) {
                     mouseHandler = new MouseHandler();
                }
                return mouseHandler;
           }

           @Override
           protected void paintComponent(Graphics g) {
                super.paintComponent(g);
                Graphics2D g2d = (Graphics2D) g.create();
                if (lastPoint != null) {
                     g2d.setColor(Color.RED);
                     g2d.fillOval(lastPoint.x - 2, lastPoint.y - 2, 4, 4);
                }
                if (currentShape != null) {
                     g2d.setColor(Color.RED);
                     g2d.draw(currentShape);
                     if (lastPoint != null && currentPoint != null) {
                          System.out.println(lastPoint + " - " + currentPoint);
                          g2d.setColor(new Color(255, 0, 0, 64));
                          g2d.draw(new Line2D.Float(lastPoint, currentPoint));
                     }
                }
                g2d.setColor(Color.BLACK);
                for (Shape shape : lstPloys) {
                     g2d.draw(shape);
                }
                g2d.dispose();
           }

           public class MouseHandler extends MouseAdapter {

                @Override
                public void mouseClicked(MouseEvent e) {
                     if (e.getButton() == MouseEvent.BUTTON1) {
                          if (e.getClickCount() == 1) {
                               Point p = e.getPoint();
                               lastPoint = p;
                               if (currentShape == null) {
                                    currentShape = new Path2D.Float();
                                    currentShape.moveTo(p.x, p.y);
                               } else {
                                    currentShape.lineTo(p.x, p.y);
                               }
                               repaint();
                          } else if (e.getClickCount() == 2) {
                               currentShape.closePath();
                               lstPloys.add(currentShape);
                               currentShape = null;
                               lastPoint = null;
                               repaint();
                          }
                     }
                }

                @Override
                public void mouseMoved(MouseEvent e) {
                     if (currentShape != null) {
                          currentPoint = e.getPoint();
                          repaint();
                     } else {
                          currentPoint = null;
                     }
                }

           }

      }

 }

You will want to the time to read through

• Performing Custom Painting
• 2D Graphics

As these will cover the basics of what you need to know to achieve what you are trying to do.

Updated

I've updated the example to include showing the line to the next point using a MosueMotionListener