java.io.File

java.io.File 是操作文件夹及文件的类，具有跨平台的特性

Constructor

　　File(String pathname)

　　　　Creates a new File instance by the given pathname string

　　FIle(File parent, String child)

　　　　Creates a new File instance from a parent abstract pathname and a child pathname string.

　　File(String parent, String child)

　　　　Creates a new File instance from a parent pathname string and a child pathname string.

        File file =  new File("E:/a.txt");
        
        File parent = new File("E:/");
        String child = "a.txt";
        file = new File(parent, child);
        
        String parentStr = "E:/";
        file = new File(parentStr, child);
        
        System.out.println(file.pathSeparator);  // ;  配置环境变量的分隔符  inux 下为 ：
        System.out.println(file.separator);   //   路径分隔符 linux下为/
        System.out.println(file);   //  E:a.txt

Method

　　boolean canWrite();     // canExective()  canRead()

　　　　Tests whether the application can read the file

　　boolean exists()

　　　　Tests whether the file(directory) is exists

　　boolean createNewFile()   

　　　　only can creat the  file not directory, if the file has exists, do nothing

　　boolean delete()

　　　　Deletes the file or directory

　　String getName()

　　　　Returns the name of the file or directory

　　File getAbsoluteFile()

　　　　Returns the absolute form of this abstract pathname

　　

File file =  new File("E:/a.txt");
        
boolean b = file.exists();   // 判断文件/文件夹是否存在
b = file.canExecute();       // 判断文件/文件夹是否可执行
b = file.canRead();            // 判断文件是否可读
        
b = file.createNewFile();       // 文件不存在则创建，存在什么都不做
b = file.delete();     // 删除文件/文件夹
        
File newFile  = file.getAbsoluteFile();   //  E:a.txt 得到绝对路径对象
String name = file.getName();   // E:a.txt 得到文件名/文件夹名  即最后一级目录

　　String getParent()

　　　　Returns the pathname string of this abstract pathname's parent, or null if this pathname does not name a parent directory

　　boolean isDirectory()

　　　　Tests whether the file denoted by this abstract pathname is a directory.

　　long length()

　　　　Returns the length of the file

　　File[] listFiles()

　　　　Returns an array of abstract pathnames

File file =  new File("E:\usefulPY");
        
String parent = file.getParent();  // E: 
boolean b = file.isDirectory();   // 判断是否是目录
long l = file.length();    // 获取文件（只能是文件）大小   
File[] fileList = file.listFiles(); // 获取此目录下文件夹及文件
//  [E:/usefulPY/1.txt,E:/usefulPY/voa.py]

　　File[]  listFiles(FileFilter filter)  //  FileFilter    This is a functional interface 

                File file =  new File("E:\usefulPY");
        
        
        // 匿名内部类实现方法
        File[] fileList = file.listFiles(new FileFilter(){

            @Override
            public boolean accept(File pathname) {
                String path  = pathname.getName();
                return path.endsWith(".txt");
            }
            
        }); // 获取此目录下文件夹及文件     [E:/usefulPY/1.txt] 
        
        // lambda 表达式
        File[] fileList = file.listFiles(pathname-> {
            String path  = pathname.getName();
            return path.endsWith(".txt");
        } );
        

　　boolean mkdirs()  // can creat muti-level directory

　　　　Creates the directory named by this abstract pathname, including any necessary but nonexistent parent directories.

　　boolean renameTo(File file)　　

boolean b = file.renameTo(new File("E:/b.txt"));  // 重命名文件或文件夹
b = file.setWritable(false);   // 修改权限

File file =  new File("E:/aa/a/a");    
b = file.mkdirs();    //  E:aaaa

recursive the directory

public static void main(String[] args) {
        
        ArrayList<File> fileList = recursiveFile(new File("E:\officFile"));
        for(File f:fileList){
            System.out.println(f);
        }
    }
public static  ArrayList<File>  recursiveFile(File file){
        
        ArrayList<File> fileList =  new ArrayList<>();
        
        if(file.exists() == false)
            return fileList;
        File[] list = file.listFiles();
        for(File f: list)
        {
            if(f.isDirectory()){    
                fileList.addAll(recursiveFile(f));    
            }else{
                fileList.add(f);        
            }
            
        }
        return fileList;
 
    }
}