Java Applet Polygon array

问题

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?

回答1:

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.

回答2:

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.

来源：https://stackoverflow.com/questions/13187872/java-applet-polygon-array