Basic File class, file class

Basic File class, file class

The role of the File class:
The Java io package defines the File class for managing files or folders.
The File class can only be used to indicate the information (attributes) of a File or folder and delete and create a File or folder.
(Content cannot be accessed)
By creating a File object, you can use a program to operate files or folders on your computer.

 

File class construction method:
File (String path): Creates a new File object using the specified path name String. The abstract path name is used to locate the path of a File or folder.
File (File parent, String path): Creates a new File object based on the parent File object and path sub-File name String.

 

Common APIs of the File class
File Operations:
Exists (): determines whether a file exists. The returned value is a Boolean value.
GetCanonicalPath (): Get the standard path name of the current file
Separator: Used to indicate path-level delimiters, which can avoid inconsistency between operators in different operating systems.
CreateNewFile (): create a file in the hard disk
Length (): length
LastModified (): Creation Time: new Date (File. lastModified ())
Delete (): delete
GetName (): Get the file or folder name

Folder operation:
Exists (): determines whether a file exists. The returned value is a Boolean value.
GetCanonicalPath (): Get the standard path name of the current file
Separator: Used to indicate path-level delimiters, which can avoid inconsistency between operators in different operating systems.
Boolean mkdir (): Create a folder
Mkdirs (): Creates a folder if the parent folder does not exist.
ListFiles (): the path name returned by this method is used to represent the array of files and directories in the directory of this abstract path name.
ListFiles (FileFilter filter): the path name returned by this method is used to represent an array of files and directories in the directory of this abstract path name, and contains a filter of the FileFilter type.
IsDirectory (): determines whether a folder is used.
DelDirectory (pp): Call the delete folder Method

1 public void testFile01 () throws IOException {2 // create a File object in the computer memory to correspond to the current folder 3 File = new file (". "); 4 System. out. println ("whether the current folder exists:" + file. exists (); 5 System. out. println ("view the path of the current folder:" + file. getCanonicalPath (); 6 // there is no direct connection with the folder in the hard disk, but there is only an object in JVM 7 File fileDemo = new File (file, "fileDemo"); 8 System. out. println ("check whether the fileDemo folder exists in the current folder:" + fileDemo. exists (); 9 if (! FileDemo. exists () {10 fileDemo. mkdir (); // create the fileDemo folder 11} 12 13 File testFile = new File (file, "aa" + File. separator + "testFile"); 14 if (! TestFile. exists () {15 // boolean flag = testFile. mkdir (); 16 // System. out. println ("creation result:" + flag); 17 testFile. mkdirs (); // create a folder. When the parent directory does not exist, the parent directory will be created first 18} 19 20 File aFile = new File (fileDemo, "a.txt"); 21 System. out. println ("whether a.txt exists in the hard disk:" + aFile. exists (); 22 if (! AFile. exists () {23 aFile. createNewFile (); // create a file on the hard disk 24} 25 System. out. println ("whether a.txt exists in the hard disk:" + aFile. exists (); 26 System. out. println ("a.txt standard path:" + aFile. getCanonicalPath (); 27 System. out. println ("a.txt file length:" + aFile. length (); 28 System. out. println ("a.txt creation time:" + new Date (aFile. lastModified (); 29/* 30 * delete a file or folder represented by a file object. If yes, true is returned. 31 * if the object represents a folder, you must ensure that the folder is empty before deleting 32 */33 aFile. delete (); 34 // failure to delete aa 35 File aa = new File (file, "aa"); 36 aa. delete (); 37}

Public void testFile02 () {File file = new File (". "); // current folder object File [] files = null; if (file. exists () {// listFiles (): view the subfolders in the current folder. If the folder path is empty, return null // if the path name does not indicate a folder or an I/O exception occurs, null files = file is returned. listFiles () ;}for (File f: files) {// getName (): Get the File or folder name System. out. println (f. getName ());}}

Public void testFile03 () throws IOException {File path = new File (". "); File pppp = new File (path," pp "+ File. separator + "ppp" + File. separator + "pppp"); File demoFile = new File (pppp, "demo.txt"); if (! Pppp. exists () {pppp. mkdirs (); // create the parent folder with the subfolders} if (! DemoFile. exists () {demoFile. createNewFile (); // create a File} File pp = new File (path, "pp"); delDirectory (pp); // call the delete folder method. If there is no File under it, it can be successful}

// Use the Traversal method to delete a folder. if there are files in the folder, delete the File to prevent the folder from being deleted. public static void delDirectory (File dir) throws IOException {if (! Dir. exists () {// if the folder does not exist, throw the runtime exception throw new RuntimeException ("folder" + dir + "");} if (! Dir. isDirectory () {// determines whether the folder throw new RuntimeException (dir + "not a directory");} File [] subs = dir. listFiles (); if (subs! = Null & subs. length> 0) {// traverses all sub-files and folders and deletes the contents. // traverses all subs for (File f: subs) {if (! F. isDirectory () {// either a folder or a file System. out. println ("file name:" + f. getName (); if (! F. delete () {// If the deletion fails, an exception is thrown. If the deletion succeeds, the system does not come in, and throw new IOException ("file cannot be deleted" + f. getName () ;}} else {// folder processing System. out. println ("Start processing Folders" + f. getName (); delDirectory (f); // call the delete folder method to delete the sub-Folder System. out. println ("The subfolder has been deleted. Start to delete this folder" + f. getName (); f. delete (); // After deleting the sub-files and sub-folders, You need to delete the current folder} dir. delete (); // delete the contents of the dir directory}

// Use the filter to filter out some files and process the public void testFile04 () {File file = new File ("src" + File. separator + "day07"); // create the file object FileFilter filter = new FileFilter () {// This method is used to define filter rules, if return true, it indicates that the returned value meets the rule is false. If return is false, it indicates that the @ Override public boolean accept (File pathname) does not comply with the rule) {// matches the content that complies with the regular expression rules if (pathname. getName (). matches (". * [.] java ") {return true;} return false ;}; // pass in the filter object and filter out the file object that does not comply with the rule. File [] paths = file. listFiles (filter); for (File f: paths) {System. out. println (f. getName ());}}