Using the paint or repaint method to paint lines over an applet JAVA

问题

I am wondering if it's possible to paint lines over an applet. I am loading the applet from an external source, but I'd like to paint lines where the cursor is on the screen.

Can someone tell me how I'd do this please?

Here's an example.

  g.drawLine(mouse.getLocation().x - 6, mouse.getLocation().y,
            mouse.getLocation().x + 6, mouse.getLocation().y);
            g.drawLine(mouse.getLocation

            ().x, mouse.getLocation().y - 6,


            mouse.getLocation().x, mouse.getLocation().y + 6);

回答1:

I am wondering if it's possible to paint lines over an applet.

Sure you can. Simply put a panel in the applet, add a mouse motion listener and draw on that panel according to the events.

Small example illustrating this

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Point;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.lang.reflect.InvocationTargetException;
import java.util.ArrayList;
import java.util.List;

import javax.swing.JApplet;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

public class TestAppletDraw extends JApplet {

    public static class MyDrawPanel extends JPanel {

        private List<Point> points = new ArrayList<Point>();

        public MyDrawPanel() {
            setBackground(Color.WHITE);
            MouseAdapter listener = new MouseAdapter() {

                @Override
                public void mouseClicked(MouseEvent e) {
                    points.clear();
                    repaint();
                }

                @Override
                public void mouseMoved(MouseEvent e) {
                    points.add(e.getPoint());
                    repaint();
                }
            };
            addMouseListener(listener);
            addMouseMotionListener(listener);
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(300, 300);
        }

        @Override
        protected void paintComponent(java.awt.Graphics g) {
            super.paintComponent(g);
            Point p1 = null;
            Point p2 = null;
            g.setColor(Color.BLUE);
            for (Point p : points) {
                p2 = p1;
                p1 = p;
                if (p1 != null && p2 != null) {
                    g.drawLine(p1.x, p1.y, p2.x, p2.y);
                }
            }
        }
    }

    protected void initUI() {
        add(new MyDrawPanel());
        validate();
    }

    @Override
    public void init() {
        super.init();
        try {
            SwingUtilities.invokeAndWait(new Runnable() {
                @Override
                public void run() {
                    initUI();
                }
            });
        } catch (InvocationTargetException e) {
            e.printStackTrace();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

}

NB: Using a buffered image instead of storing points may be more scalable over long periods of time (otherwise the points List can become gigantic) but it requires to take care of panel size increases.

来源：https://stackoverflow.com/questions/15566041/using-the-paint-or-repaint-method-to-paint-lines-over-an-applet-java

标签

java

swing

applet

awt

paint