java - 为什么我的代码会产生错误？

Question

* A simple panel for testing various parts of our game.
 * This is not part of the game.  It's just for testing.
 */
package game;

import java.awt.*;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.util.Scanner;
import javax.imageio.ImageIO;
import javax.swing.JPanel;

/**
  * A simple panel for testing various parts of our game.
  * This is not part of the game.  It's just for testing.
  */
public class TestPanel extends JPanel
{
    private static final long serialVersionUID = 1L;  // Ignore this - It's just to get rid of a warning.

    // Instance variable(s).

    private Image backdrop;

    /**
     * Constructor - loads a background image
     */
    public TestPanel ()
    {
        try
        {
             ClassLoader myLoader = this.getClass().getClassLoader();
             InputStream imageStream = myLoader.getResourceAsStream("resources/path_1.jpg");
             backdrop = ImageIO.read(imageStream);

             // You will uncomment these lines when you need to read a text file.

              InputStream pointStream = myLoader.getResourceAsStream("resources/   path_1.txt");
              Scanner s = new Scanner (pointStream);
        }
        catch (IOException e)
        {
            System.out.println ("Could not load: " + e);
        }
    }

    /**
     * This paint meethod draws the background image anchored
     * in the upper-left corner of the panel.  
     */
    public void paintComponent (Graphics g)
    {
        g.drawImage(backdrop, 0, 0, null);        
    }

    /* Override the functions that report this panel's size
     * to its enclosing container. */

    public Dimension getMinimumSize()
    {
        return new Dimension (600, 600);
    }

    public Dimension getMaximumSize()
    {
        return getMinimumSize();
    }

    public Dimension getPreferredSize()
    {
        return getMinimumSize();
    }
}

此代码针对我正在为 Java 类(class)完成的视频游戏作业。这个类仅用于测试我们的代码。在作业的指导中，我被告知要放置 try block 中存在的代码，如上所示。显然，代码应该打开我工作区文件夹中的 JPEG 图像。但是，当我尝试代码时，它只指出:

Exception in thread "main" java.lang.NullPointerException   at
 java.io.Reader.<init>(Unknown Source)  at
 java.io.InputStreamReader.<init>(Unknown Source)   at
 java.util.Scanner.<init>(Unknown Source)   at
 game.TestPanel.<init>(TestPanel.java:43)   at
 game.TestApplication.main(TestApplication.java:24)

我不太清楚 inputStream 和 classLoaders 的作用。因此，如果您对其中任何一个有任何基本信息，那就太好了。另外，我知道构造函数方法下面的其他方法中没有代码。我的作业指示没有说明我应该在这些方法中输入什么内容。

enter code here
enter code here

Answer 1

第二个文件名中有一些额外的空格:

“资源/path_1.txt”

显然这是一个错字。然后，当您使用此流调用 getResourceAsStream 时，由于这些额外的空格，它找不到您想要的文件，因此该调用返回一个空指针，该指针将被传递到扫描仪中，并最终导致NPE。