Use of the Java File class (Java for file operations)

One, File class overview

java.io.The File class is an abstract representation of file and directory names, Mainly 用于文件和目录的创建，查找，删除，重命名文件，查询文件最近的修改时间等操作.
java files and folders (directories) in the computerEncapsulated as a File class that has nothing to do with the operating system。

Two, File class content organization

1. Constant

Four static member variables:

• 1.static String pathSeparator, the path separator Windows → ；,Linux → ：
• 2.static char pathSeparatorChar, path separator Windows → ；,Linux → ：
• 3.static String separator, name separator Windows → \,Linux → /
• 4.static char separatorChar, name separator Windows → \,Linux → /

Precautions:

• 1. It is not recommended to use constants to define the path separator directly, it shouldUse File.separator instead of slash(With cross-platform features, it can adapt to multiple operating systems)
• 2.pathSeparatorChar and pathSeparator with separatorChar 与 separatorThe difference between
  the character and the pathSeparatorChar separatorChar and empty "double quotation marks" addition stars and separator pathSeparator
  • public static final String pathSeparator = "" + pathSeparatorChar;
  • public static final String separator = "" + separatorChar;

2. Construction method

File(String pathname): String is used as a parameter to create a File object.

File(String parent, String child): The first and second string are spliced ​​to create a File object.

File(File parent, String child): The first File object is spliced ​​with the second string to create a File object.

File(URI uri) creates a File object by converting the given file: URI into an abstract path name.

3. Member method

Get file (directory) information

(1) getAbsolutePath method , which returns the file绝对路径 字符串

Method information:
public String getAbsolutePath()

//创建File对象
File file = new File("D:\\我的文件\\test.txt");

//返回此File的绝对路径名字符串。
File fileAbsoluteFile = file.getAbsoluteFile();
System.out.println("文件/文件夹的绝对路径为："+ fileAbsoluteFile);

(2) getPath method , this File转换为 路径名 字符串

Information method:
public String getPath ()
File classes toString方法is 调用的getPath方法.

//将此File转换为路径名字符串。
String filePath = file.getPath();
System.out.println("文件/文件夹的构造路径为：" + filePath);

(3) The getName method returns the file represented by this File文件或目录的名称

Method information:
public String getName()
passed File对象的结尾部分.

//返回由此File表示的文件或目录的名称。
String fileName = file.getName();
System.out.println("文件/文件夹的名称为：" + fileName);

(4) length method , get the file size,文件大小以字节为单位

Method information:
public long length()
if the file 不存在, 返回 0;
如果File对象表示一个目录, then返回值是不确定的

long fileLength = file.length();
System.out.println("文件/文件夹的长度（大小）为：" + fileLength);

(5)getParent method , get the name of the parent folder

Method information:
public String getParent()

System.out.println("父文件夹名称为" + file.getParent());

(6) CanRead method , whether the file is readable.

Method information:
public boolean canRead()

System.out.println("文件是否可读？" + file.canRead());

(7) CanWrite method , whether the file can be written

Method information:
public String canWrite()

System.out.println("文件是否可写？" + file.canWrite());

(8) lastModified method , get the last modified date of the file

Method information:
public long lastModified()
用long类型的毫秒数表示 , why is the millisecond value returned? Click here .

System.out.println("文件最后修改日期为：" + file.lastModified());

Determine whether the file (directory) exists

(1) Exists method , whether the file or directory represented by this File actually exists.

Method information:
public boolean exists()

//创建对象
File dir = new File("D:\\我的文件\\");
File file = new File(dir+"test.txt");
//判断file实例是否存在
System.out.println("目录是否存在:" + dir.exists());
System.out.println("文件是否存在:" + file.exists());

(2) isDirectory method , whether this File represents a directory.

Method information:
public boolean isDirectory()

//判断是文件还是目录
System.out.println("dir是文件吗？" + dir.isFile());

(3) IsFile method , whether this File represents a file.

Method information:
public boolean isFile()
passed File对象的结尾部分.

//判断是文件还是目录
System.out.println("dir是目录吗？" + dir.isDirectory());

Create file (directory)

(1) The createNewFile method creates a new empty file if and only if the file with this name does not exist yet.

Method information:
public boolean createNewFile()
This method 存在IOException异常requires exception handling (throws, try...catch)

• When the file does not exist, create the file and return true, and return false if it exists without overwriting
• This method can only create files, not folders
• The path to create the file must exist, otherwise an exception will occur

//创建对象
File dir = new File("D:\\我的文件\\");
File file = new File(dir+"test01.txt");
//创建文件
System.out.println("是否创建:" + file.createNewFile());

(2) The mkdir method creates a directory represented by this File.

Method information:
public boolean mkdir()
只能创建单级空文件夹

• If the folder does not exist, create it and return true
• If the folder exists, return false, if the path in the constructor does not exist, it will also return false

//创建对象
File dir = new File("D:\\我的文件\\mkdir");
System.out.println("是否创建:"+dir.mkdir());

(3) The mkdirs method creates the directory represented by this File, including any necessary but non-existent parent directories.

Method information:
public boolean mkdirs() is
available创建多级文件夹

• Can only create folders (mkdir also (for example, xxx.txt will only create folders with this name instead of files))

//创建对象
File dir = new File("D:\\我的文件\\mkdirs");
System.out.println("是否创建:"+dir.mkdirs());

Delete file (directory)

(1) The delete method , delete the file or directory represented by this File.

Method information:
public boolean delete()
can delete files or folders

• Return true if the file or folder is deleted successfully
• There are files or folders in the folder return false
• File or folder path does not exist, return false
• Files deleted by this deletion method will not go to the recycle bin
  • [Note] To avoid test use is to delete important files and operate the hard disk directly instead of the "fake deletion" of Windows

//创建对象
File dir = new File("D:\\我的文件\\");
File file = new File(dir+"test.txt");
//文件的删除
System.out.println("test.java是否删除" + file.delete());
//目录的删除
System.out.println("目录是否删除" + dir.delete());