如何使图像在Java中从左向右移动

Question

so far i have created the class below, however, now i would like to insert a code to make the image slide from left to right and right to left. I would normally use the Sliding platform however it doesn't work when i try to implement it. I am still a beginner in java so i am grateful for your help.

This is the code of my Java Class:

package game;

import city.soi.platform.*;

public class Enemy extends Body implements CollisionListener{

private Game game ;

    public Enemy(Game g){
        super(g.getWorld(), new PolygonShape(-27.0f,25.0f, -27.0f,-24.0f, 25.0f,-24.0f, 26.0f,25.0f, -27.0f,25.0f));
        setImage(new BodyImage("images/enemy.png"));
        g.getWorld().addCollisionListener(this);    
        game = g;
    }

    public void collide(CollisionEvent e) {
        if (e.getOtherBody() == game.getPlayer()){
         game.getPlayer().subtractFromScore(75);
         System.out.println("You have just lossed 75 Points! Current Score =  " + game.getPlayer().getScore());
         this.destroy();
     }
  }
}

Just to be clear i would like everyone i include this class onto a platform it moves from left to right.

Many Thanks,

Moe

Answer 1

This will depend a lot on what you individual requirements, but the basic concepts will remain the same.

Any type of animation in Swing must be executed in such away that it does not block the Event Dispatching Thread. Any blocking action on the EDT will prevent any repaint request (amongst other things) from been processed.

This simple example uses a javax.swing.Timer that ticks every 40 milliseconds or so (about 25 fps) and updates the position of a small "ball"

More complex iterations would require a dedicated Thread . This makes the whole process far more complex as

1. You should never update/create/modify/change any UI component (or property that the UI may require to perform painting) from any thread other then the EDT
2. You don't control the paint process. This means a repaint may occur at anytime and if you are modifying any property/object that the paint process requires to render the state of the game, it could cause inconsistencies.

.

public class SimpleBouncyBall {

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

    public SimpleBouncyBall() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (Exception ex) {
                }

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

    public class CourtPane extends JPanel {

        private Ball ball;
        private int speed = 5;

        public CourtPane() {
            Timer timer = new Timer(40, new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    Rectangle bounds = new Rectangle(new Point(0, 0), getSize());
                    if (ball == null) {
                        ball = new Ball(bounds);
                    }
                    speed = ball.move(speed, bounds);
                    repaint();
                }
            });
            timer.setRepeats(true);
            timer.setCoalesce(true);
            timer.start();
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(100, 100);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g); 
            if (ball != null) {
                Graphics2D g2d = (Graphics2D) g.create();
                g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
                Point p = ball.getPoint();
                g2d.translate(p.x, p.y);
                ball.paint(g2d);
                g2d.dispose();
            }
        }

    }

    public class Ball {

        private Point p;
        private int radius = 12;

        public Ball(Rectangle bounds) {

            p = new Point();
            p.x = 0;
            p.y = bounds.y + (bounds.height - radius) / 2;

        }

        public Point getPoint() {
            return p;
        }

        public int move(int speed, Rectangle bounds) {

            p.x += speed;
            if (p.x + radius >= (bounds.x + bounds.width)) {

                speed *= -1;
                p.x = ((bounds.x + bounds.width) - radius) + speed;

            } else if (p.x <= bounds.x) {

                speed *= -1;
                p.x = bounds.x + speed;

            }

            p.y = bounds.y + (bounds.height - radius) / 2;

            return speed;

        }

        public void paint(Graphics2D g) {
            g.setColor(Color.RED);
            g.fillOval(0, 0, radius, radius);
        }

    }

}