Java Applet Polygon array

Question

I have a functional program that gathers coordinates with each mouse click and then draws a polygon using those coordinates. I added a feature so that when you are done drawing your polygon and it is filled in, you can then erase the screen and start again with a new shape. What I am having trouble with is figuring out a way to reset the coordinate values.

What I have now is within my actionPerformed method I Zero out my two arrays (XCoordinates and YCoordinates). Now the user can start fresh with new coordinates but now the first coordinate is (0,0). Every time I draw a shape it starts in the upper left corner haha.

I want to set the values of the array to the values it had when I originally had when I initialized the two arrays. I tried to RE-initialize the arrays withing actionPerformed but it didn't work AND I'm sure that is very bad programming practice.

Any ideas?

You might wish to show some code to go along with your description. Else, how are we to know what you may be doing wrong? — Hovercraft Full Of Eels, Nov 02 '12 at 01:15
One array of type `Point`, is more Object Oriented then parallel x-y arrays. — Mordechai, Nov 02 '12 at 01:30
Myself I'd use an `ArrayList` and would then call `clear()` on it to reset it when desired. — Hovercraft Full Of Eels, Nov 02 '12 at 01:33
@Hovercraft & M.M.'s suggestions are conceptually appealing; they can be composed with `Polygon` to leverage the latter's implementation of the `Shape` interface. — trashgod, Nov 02 '12 at 02:28

score 2 · Answer 1 · edited May 23 '17 at 11:43

2

It's tempting to manipulate the Polygon coordinate array fields directly, but you should do so only through the public API. In particular, look at these methods:

invalidate(), which "should be called after any direct manipulation of the coordinates."
reset(), which makes a polygon empty.
addPoint(), which maintains an internally consistent state.

There's a related example here.

edited May 23 '17 at 11:43

Community

1
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answered Nov 02 '12 at 02:21

trashgod

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score 2 · Answer 2 · answered Nov 02 '12 at 03:17

You're making it hard by not providing any code, but here's two takes on the idea...

Use Polygon

This basically uses a Polygon and keeps adding points to it until you press enter...

public class PolyPainter {

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

    public PolyPainter() {
        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();
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());
                frame.add(new PolyPane());
                frame.setSize(400, 400);
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    protected class PolyPane extends JPanel {

        private Polygon poly;
        private Point lastPoint;

        public PolyPane() {

            poly = new Polygon();

            InputMap im = getInputMap();
            im.put(KeyStroke.getKeyStroke(KeyEvent.VK_ENTER, 0), "clear");
            ActionMap am = getActionMap();
            am.put("clear", new AbstractAction() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    poly = new Polygon();
                    repaint();
                }
            });

            addMouseListener(new MouseAdapter() {
                @Override
                public void mousePressed(MouseEvent e) {
                    lastPoint = e.getPoint();
                    poly.addPoint(e.getX(), e.getY());
                    repaint();
                }
            });
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g); 
            Graphics2D g2d = (Graphics2D) g.create();
            g2d.draw(poly);
            if (lastPoint != null) {
                g2d.setColor(Color.RED);
                g2d.fillOval(lastPoint.x - 5, lastPoint.y - 5, 10, 10);
            }
            g2d.dispose();
        }
    }
}

Use List Of Points

This basically uses a list of points

public class PolyPainter1 {

    public static void main(String[] args) {
        new PolyPainter1();
    }

    public PolyPainter1() {
        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();
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());
                frame.add(new PolyPane());
                frame.setSize(400, 400);
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    protected class PolyPane extends JPanel {

        private List<Point> poly;
        private Point lastPoint;

        public PolyPane() {

            poly = new ArrayList<Point>(25);

            InputMap im = getInputMap();
            im.put(KeyStroke.getKeyStroke(KeyEvent.VK_ENTER, 0), "clear");
            ActionMap am = getActionMap();
            am.put("clear", new AbstractAction() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    poly.clear();
                    repaint();
                }
            });

            addMouseListener(new MouseAdapter() {
                @Override
                public void mousePressed(MouseEvent e) {
                    lastPoint = e.getPoint();
                    poly.add(lastPoint);
                    repaint();
                }
            });

        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g); 
            Graphics2D g2d = (Graphics2D) g.create();
            Polygon pg = new Polygon();
            for (Point p : poly) {
                pg.addPoint(p.x, p.y);
            }
            g2d.draw(pg);
            if (lastPoint != null) {
                g2d.setColor(Color.RED);
                g2d.fillOval(lastPoint.x - 5, lastPoint.y - 5, 10, 10);
            }
            g2d.dispose();
        }
    }
}

Personally, the first one is more efficient, as it doesn't need to construct a new Polygon object each time it does a repaint.

Java Applet Polygon array

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