Question

我试图编写一个屏幕保护程序类型的程序，但是我得到了一个我无法追踪的空指针异常。我正在浏览一个目录，我认为正在发生的事情就是“走路”。到达文件夹而不是文件，它会抛出异常。我无法解决这方面的问题！这是代码：

import java.io.File;
import java.io.IOException;
import java.util.Random;


public class Recursion {

    public void walk(String path) throws InterruptedException, IOException {

        File root = new File(path);
        File[] list = root.listFiles();
        String[] fileArray = new String[list.length];
        int i = 0;
        if (list == null) {
            return;
        }

        for (File f : list) {

            if (f.isDirectory()) {
                walk(f.getAbsolutePath());

            } else if (f.isFile()) {
                String outPath = f.getAbsolutePath();
                System.out.println("File:" + outPath);
                fileArray[i] = outPath;
                i++;

            }
        }
        for (int j = 0; j < fileArray.length; j++) {//WILL NEED TO CONVERT TO SOME FORM OF WHILE LOOP LATER
            Random randomGenerator = new Random();//Initiates random generator
            int randomInt = randomGenerator.nextInt(fileArray.length);////Limits max random to length of folder array
            String files = fileArray[randomInt];//Chooses a filename based on random number

            Imagetime go = new Imagetime();
            go.Show(files);

        }

}

}

这是系统输出和错误：

File:c:\Users\Guy\Pictures\Edited\Geography\Snowdon\From East (Capel Curig) 16-6-14 - No Cars.png
File:c:\Users\Guy\Pictures\Edited\Geography\Snowdon\From East (Capel Curig) 16-6-14.jpg
File:c:\Users\Guy\Pictures\Edited\Geography\Snowdon\From East (Capel Curig) 16-6-14.png
File:c:\Users\Guy\Pictures\Edited\Geography\Snowdon\IMG_7457.png
File:c:\Users\Guy\Pictures\Edited\Geography\Snowdon\test.png
Displaying image...c:\Users\Guy\Pictures\Edited\Geography\Snowdon\test.png
Displaying image...c:\Users\Guy\Pictures\Edited\Geography\Snowdon\IMG_7457.png
Displaying image...c:\Users\Guy\Pictures\Edited\Geography\Snowdon\IMG_7457.png
Displaying image...c:\Users\Guy\Pictures\Edited\Geography\Snowdon\From East (Capel Curig) 16-6-14.jpg
Displaying image...c:\Users\Guy\Pictures\Edited\Geography\Snowdon\From East (Capel Curig) 16-6-14 - No Cars.png
Exception in thread "main" java.lang.NullPointerException
        at screensaver.Imagetime.Show(Imagetime.java:40)
    at screensaver.Recursion.walk(Recursion.java:49)
    at screensaver.Recursion.walk(Recursion.java:31)
    at screensaver.ScreenSaver.main(ScreenSaver.java:23)
Java Result: 1
BUILD SUCCESSFUL (total time: 12 seconds)

＆＃34;显示图像.....＆＃34;来自Imagetime类。

这样做的结果是显示了初始目录中的少数文件，但是其他文件夹中没有其他文件，因为异常会使所有文件都关闭。

其他所有内容都与我的预期完全一致，但我不知道如何解决此问题。如果我删除＆＃39; walk＆＃39;为了

if(f.isDirectory()){
     walk(f.getAbsolutePath())
}

并将if条件保留为空，我根本没有显示任何图像。

有人请求帮助，这已经让我心理太久了！

提前致谢。

Answer 1

如果您的文件夹中有任何目录，则您的数组长度将长于您在阵列末尾留下一组空条目的文件数。当您的随机数击中其中一个时，您将收到此错误。我建议将数组切换到列表以消除这种情况。

找不到我的空指针 - Java / Netbeans 8中的递归

1 个答案: