How to move the image inside the JApplet in vertical line?

I have displayed an image(ball) inside the JApplet, now I want the image to move in a vertical way (up and down). The problem is I don't know how to do it.

Could someone 开发者_Python百科has an idea about this matter?

You need to set the position of that image to some calculated value (means you caculate the vertical position using time, speed and maybe other restrictions).

How you'd set that position depends on how you draw the image.

Example, based on drawing in the applet's (or a nested component's) paint(Graphics g) method:

//first calculate the y-position
int yPos += timeSinceLastPaint * speed; //increment the position
if( (speed > 0 && yPos > someMaxY) || (speed < 0 && yPos <0 ) ) {
  speed *= -1; //if the position has reached the bottom (max y) or the top invert the direction  
}


//in your paint(Graphics g) method:
g.drawImage(image, yPos, x, null);

Then you'd have to constantly repaint the applet.

More information on animations in applets can be found here: http://download.oracle.com/javase/tutorial/uiswing/components/applet.html

another example for javax.swing.Timer with moving Ojbects created by paintComponent(Graphics g), and I have lots of Start, not some blurred Mikado :-)

import java.awt.*;
import java.awt.event.*;
import java.util.*;
import javax.swing.*;
import javax.swing.Timer;

public class AnimationBackground {

    private Random random = new Random();
    private JFrame frame = new JFrame("Animation Background");
    private final MyJPanel panel = new MyJPanel();
    private JLabel label = new JLabel("This is a Starry background.", JLabel.CENTER);
    private JPanel stopPanel = new JPanel();
    private JPanel startPanel = new JPanel();

    public AnimationBackground() {
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setResizable(false);
        panel.setBackground(Color.BLACK);
        for (int i = 0; i < 50; i++) {
            Star star = new Star(new Point(random.nextInt(490), random.nextInt(490)));
            star.setColor(new Color(100 + random.nextInt(155), 100 + random.nextInt(155), 100 + random.nextInt(155)));
            star.setxIncr(-3 + random.nextInt(7));
            star.setyIncr(-3 + random.nextInt(7));
            panel.add(star);
        }
        panel.setLayout(new GridLayout(10, 1));
        label.setForeground(Color.WHITE);
        panel.add(label);
        stopPanel.setOpaque(false);
        stopPanel.add(new JButton(new AbstractAction("Stop this madness!!") {

            private static final long serialVersionUID = 1L;

            @Override
            public void actionPerformed(ActionEvent e) {
                panel.stopAnimation();
            }
        }));
        panel.add(stopPanel);
        startPanel.setOpaque(false);
        startPanel.add(new JButton(new AbstractAction("Start moving...") {

            private static final long serialVersionUID = 1L;

            @Override
            public void actionPerformed(ActionEvent e) {
                panel.startAnimation();
            }
        }));
        panel.add(startPanel);
        frame.add(panel);
        frame.pack();
        frame.setLocation(150, 150);
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {

            @Override
            public void run() {
                AnimationBackground aBg = new AnimationBackground();
            }
        });
    }

    private class Star extends Polygon {

        private static final long serialVersionUID = 1L;
        private Point location = null;
        private Color color = Color.YELLOW;
        private int xIncr, yIncr;
        static final int WIDTH = 500, HEIGHT = 500;

        Star(Point location) {
            int x = location.x;
            int y = location.y;
            this.location = location;
            this.addPoint(x, y + 8);
            this.addPoint(x + 8, y + 8);
            this.addPoint(x + 11, y);
            this.addPoint(x + 14, y + 8);
            this.addPoint(x + 22, y + 8);
            this.addPoint(x + 17, y + 12);
            this.addPoint(x + 21, y + 20);
            this.addPoint(x + 11, y + 14);
            this.addPoint(x + 3, y + 20);
            this.addPoint(x + 6, y + 12);
        }

        public void setColor(Color color) {
            this.color = color;
        }

        public void move() {
            if (location.x < 0 || location.x > WIDTH) {
                xIncr = -xIncr;
            }
            if (location.y < 0 || location.y > WIDTH) {
                yIncr = -yIncr;
            }
            translate(xIncr, yIncr);
            location.setLocation(location.x + xIncr, location.y + yIncr);
        }

        public void setxIncr(int xIncr) {
            this.xIncr = xIncr;
        }

        public void setyIncr(int yIncr) {
            this.yIncr = yIncr;
        }

        public Color getColor() {
            return color;
        }
    }

    private class MyJPanel extends JPanel {

        private static final long serialVersionUID = 1L;
        private ArrayList<Star> stars = new ArrayList<Star>();
        private Timer timer = new Timer(20, new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {
                for (Star star : stars) {
                    star.move();
                }
                repaint();
            }
        });

        public void stopAnimation() {
            if (timer.isRunning()) {
                timer.stop();
            }
        }

        public void startAnimation() {
            if (!timer.isRunning()) {
                timer.start();
            }
        }

        @Override
        public void addNotify() {
            super.addNotify();
            timer.start();
        }

        @Override
        public void removeNotify() {
            super.removeNotify();
            timer.stop();
        }

        MyJPanel() {
            this.setPreferredSize(new Dimension(512, 512));
        }

        public void add(Star star) {
            stars.add(star);
        }

        @Override
        public void paintComponent(Graphics g) {
            super.paintComponent(g);
            ((Graphics2D) g).setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
            for (Star star : stars) {
                g.setColor(star.getColor());
                g.fillPolygon(star);
            }
        }
    }
}

How to move the image inside the JApplet ..?

Pretty much exactly the same way you might do it in a JFrame, JComponent or JPanel or...

Or to put that another way, nothing to do with applets and everything to do with Graphics2D. For more details, see the 2D Graphics Trail of the Java Tutorial.

When you've figured how to move an image and paint it to a Graphics2D, implement that logic in a JComponent or JPanel's paintComponent(Graphics) method and drop the component with moving image into a JApplet or JFrame (or a JPanel etc.).

For the animation side of it, use a javax.swing.Timer as seen in this example. This example does not extend any component. Instead, it creates a BufferedImage and adds it to a JLabel that is displayed to the user. When the timer fires, the code grabs the Graphics object of the image, and proceeds from there to draw the bouncing lines.

import java.awt.image.BufferedImage;
import java.awt.event.*;
import java.awt.geom.*;
import java.awt.*;
import javax.swing.*;
import java.util.Random;

class LineAnimator {

    public static void main(String[] args) {
        final int w = 640;
        final int h = 480;
        final RenderingHints hints = new RenderingHints(
            RenderingHints.KEY_ANTIALIASING,
            RenderingHints.VALUE_ANTIALIAS_ON
            );
        hints.put(
            RenderingHints.KEY_ALPHA_INTERPOLATION,
            RenderingHints.VALUE_ALPHA_INTERPOLATION_QUALITY
            );
        final BufferedImage bi = new BufferedImage(w,h, BufferedImage.TYPE_INT_ARGB);
        final JLabel l = new JLabel(new ImageIcon(bi));
        final BouncingLine[] lines = new BouncingLine[100];
        int factor = 1;
        for (int ii=0; ii<lines.length; ii++) {
            lines[ii] = new BouncingLine(w*factor,h*factor);
        }
        final Font font = new Font("Arial", Font.BOLD, 30);
        ActionListener al = new ActionListener() {

            int count = 0;
            long lastTime;
            String fps = "";
            private final BasicStroke stroke = new BasicStroke(6);

            public void actionPerformed(ActionEvent ae) {
                count++;
                Graphics2D g = bi.createGraphics();
                g.setRenderingHints(hints);
                g.setColor(new Color(55,12,59));
                g.fillRect(0,0,w,h);
                g.setStroke(stroke);

                for (int ii=0; ii<lines.length; ii++) {
                    lines[ii].move();
                    lines[ii].paint(g);
                }

                if ( System.currentTimeMillis()-lastTime>1000 ) {
                    lastTime = System.currentTimeMillis();
                    fps = count + " FPS";
                    count = 0;
                }
                g.setColor(Color.YELLOW);
                g.setFont(font);
                g.drawString(fps,5,h-5);

                l.repaint();
                g.dispose();
            }
        };
        Timer timer = new Timer(25,al);
        timer.start();

        JOptionPane.showMessageDialog(null, l);
        //System.exit(0);
        timer.stop();
    }
}

class BouncingLine {
    private final Color color;
    private static final Random random = new Random();
    Line2D line;
    int w;
    int h;
    int x1;
    int y1;
    int x2;
    int y2;

    BouncingLine(int w, int h) {
        line = new Line2D.Double(random.nextInt(w),random.nextInt(h),random.nextInt(w),random.nextInt(h));
        this.w = w;
        this.h = h;
        this.color = new Color(
            random.nextInt(255)
            ,random.nextInt(255)
            ,random.nextInt(255)
            ,64+random.nextInt(128)
            );
        x1 = (random.nextBoolean() ? 1 : -1);
        y1 = (random.nextBoolean() ? 1 : -1);
        x2 = -x1;
        y2 = -y1;
    }

    public void move() {
        int tx1 = 0;
        if (line.getX1()+x1>0 && line.getX1()+x1<w) {
            tx1 = (int)line.getX1()+x1;
        } else {
            x1 = -x1;
            tx1 = (int)line.getX1()+x1;
        }
        int ty1 = 0;
        if (line.getY1()+y1>0 && line.getY1()+y1<h) {
            ty1 = (int)line.getY1()+y1;
        } else {
            y1 = -y1;
            ty1 = (int)line.getY1()+y1;
        }
        int tx2 = 0;
        if (line.getX2()+x2>0 && line.getX2()+x2<w) {
            tx2 = (int)line.getX2()+x2;
        } else {
            x2 = -x2;
            tx2 = (int)line.getX2()+x2;
        }
        int ty2 = 0;
        if (line.getY2()+y2>0 && line.getY2()+y2<h) {
            ty2 = (int)line.getY2()+y2;
        } else {
            y2 = -y2;
            ty2 = (int)line.getY2()+y2;
        }
        line.setLine(tx1,ty1,tx2,ty2);
    }

    public void paint(Graphics g) {
        Graphics2D g2 = (Graphics2D)g;
        g2.setColor(color);
        //line.set
        g2.draw(line);
    }
}

Update 1

I want to do it in JApplet(1) using the image(2), is it possible(3)?

1. The examples by mKorbel and myself feature either an image in a JLabel or custom rendering in a JPanel. In our case, we added the components to a JOptionPane & a JFrame. Either example could be just as easily added to a JApplet, or a JDialog, or as part of another panel, or.. See the Laying Out Components Within a Container lesson & Using Top-Level Containers in the Java Tutorial for more details.
2. Instead of the stars or lines in our examples, ..paint your image. My example goes so far as to demonstrate how to get the position to bounce around within the bounds of the container.
3. Sure it is possible, but "Batteries not included". Our intention is to give you some ideas that you can then adapt to your bouncing ball applet. I doubt anyone is going to create an example for you, using balls, in an applet. Though if you post an SSCCE that shows your intent and what you tried, I (and others) would often run with that source. If you want more specific answers, ask a more specific SSCCE. ;)

I want to do it in JApplet.

Why not both? You can have a hybrid application/applet as shown in this animation.