File class: directory traversal

File class traversal (folder) directory function
public String[] list(): returns a String array, representing all sub-files or directories in the
File directory public File[] listFiles(): returns a File array, representing the File directory All subfiles or directories in

注意：
    list方法和listFiles方法遍历的是构造方法中给出的目录
    如果构造方法中给出的目录的路径不存在，会抛出空指针异常
    如果构造方法中给出的路径不是一个目录，也会抛出空指针异常

Code:

public class Demo06File {
    
    
    public static void main(String[] args) {
    
    
        show02();
    }

    /*
         public File[] listFiles() : 返回一个File数组，表示该File目录中的所有的子文件或目录
         遍历构造方法中给出的目录，或获取目录中所有的文件/文件夹，把文件/文件夹封装为File对象，多个File对象存储到file数组中
    */
    private static void show02() {
    
    
        File file = new File("D:\\Learn\\IdeaProjects\\sy\\day08_FileAndRecursion");
        File[] files = file.listFiles();
        for (File f : files) {
    
    
            System.out.println(f);
        }
    }

    /*
        public String[] list() : 返回一个String数组，表示该File目录中得所有子文件或目录
        遍历构造方法中给出的目录，会获取目录中所有文件/文件夹的名称，把爱获取到的多个名称存储到一个String类型的数组中
    */
    private static void show01() {
    
    
        //File file = new File("D:\\Learn\\IdeaProjects\\sy\\day08_FileAndRecursion\\1.txt");//NullPointerException
        //File file = new File("D:\\Learn\\IdeaProjects\\sy\\day08_F");//NullPointerException
        File file = new File("D:\\Learn\\IdeaProjects\\sy\\day08_FileAndRecursion");
        String[] arr = file.list();
        for (String fileName:arr) {
    
    
            System.out.println(fileName);
        }
    }
}

Program demonstration: