为什么我看不到文件？

Question

hi i want to make simple game. but before i create game logic, i got a problem. as i mentioned on the title. i can't read jpg file. i got this error message "Can't read input file!". I know it's from e.getMessage(). But that's all. I really don't know WHY this happened. In the missilegame package, there is 3 jpg files already.

so, here is code.

package missilegame;
import java.awt.Graphics;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.awt.image.BufferedImage;
import java.io.File;

import javax.imageio.ImageIO;
import javax.swing.JFrame;
import javax.swing.JPanel;

class GraphicObject {
BufferedImage img = null;
int x, y = 0;

public GraphicObject(String name) {
    try {
        img = ImageIO.read(new File(name));
    } catch (Exception e) {
        System.out.println(e.getMessage());
        System.exit(0);
    }
}

public void update() {
}

public void draw(Graphics g) {
    g.drawImage(img, x, y, null);
}

public void keyPressed(KeyEvent event) {

}

public void keyPressed(KeyEvent event, int x, int y) {
    // TODO Auto-generated method stub

}
}

class Missile extends GraphicObject {
    boolean launched = false;

    public Missile(String name) {
        super(name);
        y = -200;
    }

    @Override
    public void update() {
        if (launched)
            y -= 1;
        if (y < -100) {
            launched = false;
        }
    }

    @Override
    public void keyPressed(KeyEvent event, int x, int y) {
        if (event.getKeyCode() == KeyEvent.VK_SPACE) {
            launched = true;
            this.x = x;
            this.y = y;
        }
    }
}

class Enemy extends GraphicObject {
    int dx = -10;

    public Enemy(String name) {
        super(name);
        x = 500;
        y = 0;
    }

    public void update() {
        x += dx;
        if (x < 0) {
            dx = +10;
        }
        if (x > 500)
            dx = -10;
    }

}

class SpaceShip extends GraphicObject {
    public SpaceShip(String name) {
        super(name);
        x = 150;
        y = 350;
    }

    @Override
    public void keyPressed(KeyEvent event) {
        if (event.getKeyChar() == KeyEvent.VK_LEFT) {
            x -= 10;
        }
        if (event.getKeyChar() == KeyEvent.VK_RIGHT) {
            x += 10;
        }
        if (event.getKeyChar() == KeyEvent.VK_UP) {
            y -= 10;
        }
        if (event.getKeyChar() == KeyEvent.VK_DOWN) {
            y += 10;
        }
    }
}

class MyGamePanel extends JPanel implements KeyListener {
    Enemy enemy;
    SpaceShip spaceShip;
    Missile missile;

    public MyGamePanel() {
        this.addKeyListener(this);
        this.requestFocus();
        setFocusable(true);

        enemy = new Enemy("./enemy.jpg");
        spaceShip = new SpaceShip("./spaceship.jpg");
        missile = new Missile("./missile.jpg");
        class MyThread extends Thread {
            public void run() {
                while (true) {
                    enemy.update();
                    spaceShip.update();
                    missile.update();
                    repaint();
                    try {
                        Thread.sleep(50);
                    } catch (Exception e) {
                    }
                }
            }

        }
        Thread t = new MyThread();
        t.start();
    }

    @Override
    public void paint(Graphics g) {
        super.paint(g);
        enemy.draw(g);
        spaceShip.draw(g);
        missile.draw(g);
    }

    @Override
    public void keyTyped(KeyEvent e) {
    }

    @Override
    public void keyPressed(KeyEvent e) {
        spaceShip.keyPressed(e);
        missile.keyPressed(e,spaceShip.x,spaceShip.y);
    }

    @Override
    public void keyReleased(KeyEvent e) {
    }

}

public class MissileGame extends JFrame {
    public MissileGame() {
        setTitle("MY Game");
        add(new MyGamePanel());
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setSize(500, 500);
        setVisible(true);
    }

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

}

Answer 1

In the missilegame package, there is 3 jpg files already.

But your code doesn't read from the missilegame package. It reads a file in the current directory, on the file system. The current directory is the directory from where the java command is executed. And your files are not (necessarily) on the file system. They're resources embedded in the application, that should be loaded with the class loader.

Replace

img = ImageIO.read(new File(name));

by

img = ImageIO.read(GraphicObject.class.getResourceAsStream("/missilegame/" + name));

and replace "./enemy.jpg" by "enemy.jpg" .