Java--file class, Recursive

first, the file classget path or directory separator

public static void Main (string[] args) {//file class static member variable//system-related path delimiter String separator = file.pathseparator; SYSTEM.OUT.PRINTLN (separator);//is a semicolon, directory partition of   Linux://System-related default name delimiter separator = File.separator; SYSTEM.OUT.PRINTLN (separator);//right \  directory name split  Linux/}

1, 3 kinds of construction methods

/* *  file (file parent,string child) *  pass path, pass file type parent path, string subpath *  Benefit: Parent path is file type, parent path can call file class method directly */public static void Function_2 () {File parent = new File ("D:"); File File = new file (parent, "Eclipse"); System.out.println (file);} /* *  File (string parent,string Child) *  pass path, pass string parent path, string subpath *  benefit: Operation parent and subpath separately */public static void function _1 () {File File = new file ("D:", "Eclipse"); System.out.println (file);} /* *  file (String pathname) *  Pass path name: can write to a folder, can write to a file *  c:\\abc   C:\\abc\\demo.java *  Encapsulates a path to the file type object */public static void function () {File File = new file ("D:\\eclipse"); System.out.println (file);}

2. Create a file

/* * File  creation function *  boolean createnewfile () *  creates a file path and file name, given in the file constructor method *  file already exists, no longer created, return value is false * /public static void function () throws Ioexception{file file = new file ("C:\\a.txt"); Boolean B = File.createnewfile (); System.out.println (b);}

3. Create a folder

/* *  File Create folder function *  boolean mkdirs () create a multi-tiered folder * The  path created is also given in the file construction method *  folder already exists, no longer created, and the return value is False */public static void Function_1 () {File File = new file ("C:\\abc"); Boolean B = File.mkdirs (); System.out.println (b);}

4. Delete files and folders

/* *  the Delete function of the file class *  Boolean Delete () * Delete  the file or the folder, given in the file constructor method *  Delete succeeded return true, delete failed return false *  Delete method, Do not walk the Recycle Bin, remove directly from the hard drive *  Delete risky, operation need to be cautious */public static void Function_2 () {File File = new file ("C:\\a.txt"); Boolean B = File.del Ete (); System.out.println (b);}

5. Get the name of the file or folder

/* *  File class get function *  String getName () *  returns the filename represented in the path or folder name * Gets the name of the  last part of the path */public static void function () { File File = new file ("D:\\eclipse\\eclipse.exe"); String name = File.getname (); SYSTEM.OUT.PRINTLN (name);}

6. Get the number of bytes in the file

/* * File class get function * long length () * Returns the number of bytes of the file represented in the path */public static void Function_1 () {File File = new file ("D:\\eclipse\\eclip Se.exe "); Long length = File.length (); System.out.println (length);}

7. Get the absolute path

/* * File class Get function * String GetAbsolutePath () returns a String Object * file   getabsolutefile () returns the file object */public static void Function_2 () {File File = new file ("src"); File absolute = File.getabsolutefile (); System.out.println (absolute);}

8. Get the parent path

/* * File class Get function * String getParent () return string Object * file Getparentfile () return file Object * Get parent path */public static void Function_3 () {F ile file = new file ("D:\\eclipse\\eclipse.exe"); File parent = File.getparentfile (); SYSTEM.OUT.PRINTLN (parent);}

9. Determine if the path exists

/* *  file Judgment function *  Boolean exists () *  determine if the package path exists in the file construction method *  exists returns true, there is no return false */public static void function () {File File = new file ("src"); Boolean B = file.exists (); System.out.println (b);}

10. Decide whether to file/folder

/* *  file Judgment function *  boolean isdirectory () *  determines whether the path encapsulated in the file construction method is not a folder *  if it is a folder, returns True, not the file returns false *   *  boolean isfile () *  determines whether the path encapsulated in the file construction method is not a */public static void Function_1 () () {filename = new file ("d:\\eclipse\\ Eclipse.exe "), if (File.exists ()) {Boolean b = File.isdirectory (); System.out.println (b);}}

11. Traversing all the files in the directory

/* *  the FETCH function of the file class *  file[] listfiles () *  gets the file and folder name (traversing a directory) in the path encapsulated in the file construction method *  Returns the full path of the directory or file */ public static void Function_1 () {File File = new file ("D:\\eclipse"); file[] Filearr = File.listfiles (); for (file F:filearr) {System.out.println (f);}} /* *  the FETCH function of the file class *  string[] List () *  gets the file and folder name (traversing a directory) in the path encapsulated in the file construction method *  returns only the name */public static void function () {File File = new file ("C:"); string[] Strarr = File.list (); System.out.println (strarr.length); for (String Str:strarr) {System.out.println (str);}}

12. File Filter

We need to write a filter ourselves.

Import Java.io.file;import java.io.filefilter;/* *  Custom filter *  implement FileFilter interface, override abstract method */public class Myfilter Implements Filefilter{public Boolean accept (file pathname)  {/* * pathname is also the full path of the file * C:\\demo\\1.txt * To determine the path, if Is a Java file that returns True, not a Java file, and returns false * The suffix end of the file is. java *///string name = Pathname.getname (); return Pathname.getname (). EndsWith (". Java");}}

Then add its anonymous object to the Listfiles

Import java.io.file;/* * File class, get  filter *  When you traverse the directory, you can only get the file that satisfies the condition if necessary *  Traverse directory Method Listfiles () overloaded form *  Listfiles (filefilter Filter) interface type *  transitive FileFilter Interface implementation class *  Custom FileFilter Interface implementation class, overriding abstract method, *  Interface implementation Class object passed to Traverse method Listfiles */public class FileDemo1 {public static void main (string[] args) {File file = new file ("C:\\demo") ; file[] Filearr = file.listfiles (New Myfilter ()); for (file F:filearr) {System.out.println (f);}}}

Second, recursion

Example:

/* * Method  Recursive Call *    method itself calls itself * suitable for, the method of the principal of the  operation is not changed, but when running, the parameters of the participating operation will change *  Note: *     recursive must have an exit, you must be able to stop the program *     Recursive times cannot be too much *     construction method, prohibit recursive */public class Diguidemo {public static void main (string[] args) {/*int sum = getsum (3); SYSTEM.OUT.PRINTLN (sum); */system.out.println (Getjiecheng (5)); System.out.println (GETFBNQ (12));}  /*  method recursive, computes Fibonacci sequence *   */public static int getfbnq (int month) {if (month = = 1) return 1;if (month = = 2) return 1;return GETFBNQ (month-1) +getfbnq (month-2);} /  * *  calculate factorial 5! *   5*4*3*2*1 */public static int Getjiecheng (int n) {if (n = = 1) return 1;return n * Getjiecheng (n-1);} /* *  calculate 1+2+3+100 and = 5050 *  Calculation rule: *    n+ (n-1) + (n-2) *    100+ (100-1) + (99-1) + ... 1 */public static int getsum (int n) {if (n = = 1) return 1;return n + getsum (n-1);}}

If we want to traverse all the files in the directory, we can use this method

/* *  defines the method that implements the full traversal of the directory */public static void Getalldir (File dir) {System.out.println (dir);//Call Method Listfiles () to the directory, Dir to traverse file[] Filearr = Dir.listfiles (); for (File F:filearr) {///Determine the path of the variable F is not a folder if (F.isdirectory ()) {//is a directory, Going to traverse this directory//This method, Getalldir, is to give a directory to traverse//continue to call Getalldir, pass his directory getalldir (f);} Else{system.out.println (f);}}

Java--file class, Recursive