java - Eclipse 错误，平台游戏

Question

我的代码有问题。我刚刚开始使用 Eclipse。目前，我正在使用 Java 开发一款平台游戏。我在使用 Homestuck 代码时遇到问题。它位于 public static void main(String[] args) 下面。谢谢大家的帮助!

错误:

Exception in thread "main" java.lang.IllegalArgumentException: input == null!
    at javax.imageio.ImageIO.read(ImageIO.java:1388)
    at projectOne.<init>(projectOne.java:31)
    at projectOne.main(projectOne.java:104)

代码:

 import java.awt.*; 
import java.awt.event.*;
import java.awt.image.BufferedImage;
import java.io.IOException;
import javax.imageio.ImageIO;
import javax.swing.*;

public class projectOne extends JPanel
{   
    /**
     * 
     */
    private static final long serialVersionUID = 1L;

    GameEvents gameEvents = new GameEvents();
    Timer gameTimer = new Timer(1, gameEvents);
    int i = 0; 
    int horizontalposition = 500;
    int verticalposition = 500;
    BufferedImage Picture;
    //Don't forget to declare your variables!


    projectOne()
    {
        gameTimer.start();
        this.addKeyListener(gameEvents);

        try 
        {
            Picture = ImageIO.read(getClass().getResource("Homestuck.gif"));
            //The format for this is Picture = ImageIO.read(getClass().getResource("NameOfFile.typeoffile"));
        }
        catch (IOException e)
        {
            System.out.println("Pictures failed to load");
        }
    }

    @Override
    protected void paintComponent(Graphics g)
    {
        g.setColor(Color.blue);
        g.fillRect(0,0,this.getWidth(), this.getHeight());
        g.setColor(Color.red);
        ///g.drawImage(Picture, horizontalposition, verticalposition, 100, 150, null);
        g.drawImage(Picture, 50, 100, 500, 600, null);

        //Here's the format you must follow when drawing simple Java Graphics objects
        //g.fillOval(horizontal location, vertical location, width, height)
    }

    public class GameEvents implements ActionListener, KeyListener
    {

        @Override
        public void actionPerformed(ActionEvent arg0) 
        {
            repaint();
        }

        @Override
        public void keyPressed(KeyEvent key) //stuff inside here happens when a key is pressed
        {
            if(key.getKeyChar()=='d')
            {
                horizontalposition=horizontalposition+20;
            }
            if(key.getKeyChar()=='s')
            {
                verticalposition=verticalposition+20;
            }
            if(key.getKeyChar()=='w')
            {
                verticalposition=verticalposition-20;
            }
            if(key.getKeyChar()=='a')
            {
                horizontalposition=horizontalposition-20;
            }
            if(horizontalposition<0)
            {
                horizontalposition=0;
            }
            System.out.println(key.getKeyChar());
            System.out.println('d');
        }

        @Override
        public void keyReleased(KeyEvent arg0) {

        }

        @Override
        public void keyTyped(KeyEvent arg0) {

        }

    }
    public static void main(String[] args)
    {
        JFrame f = new JFrame("Java Graphics Example Project");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        projectOne p = new projectOne();
        f.setSize(1500,700);
        f.add(p);
        f.setVisible(true);
        p.requestFocusInWindow();
    }

}

Answer 1

在这一行

Picture = ImageIO.read(getClass().getResource("Homestuck.gif"));

getResource 调用必须返回 null。我建议将其隔离为局部变量，以便更容易调试:

File imageFile = getClass().getResource("Homestuck.gif");
if (imageFile == null) {
  //consider throwing an exception here
} else {
  Picture = ImageIO.read(imageFile);
}