Day_ 17 IO stream file class

Day_17 Lecture notes

A recursive algorithm

 recursive  :  Progressive regression 
	 The embodiment in the code :  Call the method itself inside the method 
	
 Cases in life :
	 Once upon a time there was a mountain , There is a temple in the mountain , There is an old monk in the temple , The old monk tells a story to the young monk ...
         Once upon a time there was a mountain , There is a temple in the mountain , There is an old monk in the temple , The old monk tells a story to the young monk ...
        	 Once upon a time there was a mountain , There is a temple in the mountain , There is an old monk in the temple , The old monk tells a story to the young monk ...
        		 Once upon a time there was a mountain , There is a temple in the mountain , There is an old monk in the temple , The old monk tells a story to the young monk ...
        
     Learn programming  ->  To make money  ->  Marry a daughter-in-law  ->  Give birth to a baby .. 
         Learn programming  ->  To make money  ->  Marry a daughter-in-law  ->  Give birth to a baby ..  
        	 Learn programming  ->  To make money  ->  Marry a daughter-in-law  ->  Give birth to a baby ..  
        		 Learn programming  ->  To make money  ->  Marry a daughter-in-law  ->  Give birth to a baby ..  
     Russian Dolls , File traversal     

The premise of recursive algorithm

// Find the rules first 
1.  Methods must be defined 
2.  There must be an exit 
3.  The defined method must have formal parameters 
4.  When calling the method itself inside the method , The parameters passed in should be changed  -->  Change should go in the direction of Export 
5.  Don't recurse too many times 

Recursive memory graph

The principle of quick sorting

File class

File class  :   Classes for all files and folders on your computer 

 Conclusion  :  There are either files or folders in the computer 

File Class constructor and custom constants

*File(String pathname) :  Pass in a file / Folder path , Give Way File Object points to the file / Folder ;
    
File(String parent, String child) :  Express in the form of child parent path File object  (String Express )
*File(File parent, String child) :  Express in the form of child parent path File object  ( Parent path File The formal representation of objects )    
    
//File Object creation ,File Only point to files and folders at the end of the path , Does not represent the entire path  
    
    File What does object creation do :
        1.  You create an object 
        2.  Opened up memory space 
        3.  Give Way file Object points to the file at the end of the path / Folder 
        // File does not exist, no new file was created 
        
File.pathSeparator = ;
File.pathSeparatorChar = ;
File.separator = \
File.separatorChar = \        

File Class creation

* boolean createNewFile():  create a file  

boolean mkDir():  Create a single level folder 
* boolean mkDirs():  Create single level folders or multi-level folders 

Relative path and absolute path

// When the files and folders you want to represent are under the project path , You can use relative paths to represent files / Folder path  -->  Simplify writing 

 Absolute path  :  You can definitely find the file / Path to folder  -->  The full path 
	 characteristic  :  Start with a drive letter 
	
// Relative paths  :  Understand references  IDEAEclipse The starting point of the relative path of the software : Project
 Relative paths  : 	 Take the reference as the starting point , Look for files in the path / Folder 
	 characteristic  :  Don't start with a drive letter 

 use express delivery :
 Absolute path  :  The earth :\\ Asia \\ China \\ hubei \\ wuhan \\ Jiangxia \\ Maodian Shanzhong road \\ East Lake network Valley \\6 building \\4 floor \\ Silicon Valley \\402\\ Tan bin 
 Relative paths  : // object of reference :  East Lake network Valley 
	6 building \\4 floor \\ Silicon Valley \\402\\ Tan bin 

File Class delete function

boolean delete():  Delete file / Folder ,  Don't go to the recycle bin !!

File Class

* String getName() :  get files / Name of the folder 
* long length() :  Get file size ( Number of bytes taken )
 
  String getAbsolutePath() :  Returns... As a string file Object points to the file / Absolute path to folder 
  File getAbsoluteFile() :  With File Object's form return file Object points to the file / Absolute path to folder     
  
  String getParent()  :  Returns... As a string file Object points to the file / The parent path of the folder 
  File getParentFile()  :  With File Object's form return file Object points to the file / The parent path of the folder 
  
  String getPath()  :  Get create File Object time , Incoming files / Path to folder (File Class toString Method is called internally getPath)
     
   long lastModified() :  obtain File Object points to the file / The last time the folder was modified  ->  Millisecond value   

File Class

* boolean exists() :  Judge File Object points to the file / Does the folder exist !!
* boolean isFile() :  Judge File Object points to the file / Whether the folder is a file 
* boolean isDirectory() :  Judge File Object points to the file / Whether the folder is a folder    

boolean isAbsolute()  :  Judgment creation File Object, whether the absolute path is passed in 
boolean isHidden() :  Judge file Object points to the file / Whether the folder is a hidden file / Folder 

Folder traversal function

* File[] listFiles() :  Put all the files in a folder / Folder get , Deposit to File[] Array  ->  Only the current level folder can be obtained 

 If file Object refers to a file , Then the return value of the method is null -->  A null pointer exception occurred 
 If file Object points to an empty folder , Then the method will return a content of 0 Empty array of   ->  There will be no null pointer exceptions 

* File[] listFiles(FileFilter filter)  
    FileFilter filter:  Folder filter  -->  Interface 
    	 There is and only one abstract method : boolean accept(File file) ->  Rewritten is right file Object makes some kind of judgment 
    		 If the return value is true, adopt  /  If the return value is false, Not through 

I/O summary

I/O flow   technology  :  Realized Java Data interaction between code and files on hard disk  -->  Permanent storage of data 
I : input ->  Input 
O : output ->  Output 
 flow  :  Flow 

 Find out when to use the input stream / When to use the output stream  ?   object of reference :  At present Java file 
     Code data  --->  In the file  :  Output stream 
     The contents of the document  --->  In the code  :  Input stream 
    
I / O  Classification of flows  :     
	 Flow direction classification  :  Input and output streams   Input/Reader  and  Output/Writer
	 File type classification of operation : 
		 Byte file ( All files in the computer are byte files ) :  With Stream ending  ->  Byte stream ;
		 Character file ( There is a kind of file in byte file , The file is full of characters  -> txt,java,xml,html,js,md....) :  With Reader/Writer The flow at the end  -->  Character stream 
			// How to distinguish character files  :  use windows The built-in Notepad tool opens without " The statement " The file of is character file 
			
InputStream :  Byte input stream 
BufferedWriter :  Efficient character output stream 
OutputStreamWriter :  Character output stream  ->  Converted flow :  A stream that converts a byte stream into a character stream 
	//  The essence of character stream is  :  Byte stream  +  Coding format 

Byte stream architecture

 The root node of the byte stream : InputStream/OutputStream ->  abstract class 

 Subclass  :
 File byte stream ( Normal byte stream ) : FileInputStream/FileOutputStream
 Efficient byte stream : BufferedInputStream/BufferedOutputStream

FileOutputStream

FileOutputStream :  File byte output stream 

 Construction method :
	FileOutputStream(String name) :  The string type path of the incoming file , Let the byte output stream object point to this file ;
    FileOutputStream(File file) :  Of the incoming file File Type path , Let the byte output stream object point to this file ; 
    
     What does the creation of byte output stream object do :
        1.  You create an object 
        2.  Opened up memory space 
        3.  If the file does not exist, it will help you create the file , If the file exists, a new file will be created to overwrite the original file 
        4.  Let the output stream object point to the file at the end of the path  ( Here can only be files )

FileOutputStream How to write data

 How to write data  : void write ->  It's written in bytes 

	 * void write(int b) :  Write one byte at a time 
 	 void write(byte[] b)  :  Write an entire byte array at a time 
     * void write(byte[] b, int off, int len)  :  Write part of a byte array one at a time 
     	int off -> int startIndex :  Starting index 
     	int length ->  Write a few 
     	
     How to write a string  ? String ->  Byte array 
        byte[] getBytes()
     How to write line breaks  ?  "\r\n".getBytes()
     How to add  ? boolean append  Add write switch 
        FileOutputStream(String name, boolean append)
        FileOutputStream(File file, boolean append)     	

FileInputStream

FileInputStream :  Normal byte input stream 

 Construction method :     // The file pointed to by the input stream must exist !!
	FileInputStream(String name) 
    FileInputStream(File file)   
        // The input stream has no additional read 

FileInputStream How to read data

 How to read data  : int read ->  Read bytes 
	* int read() :  Read one byte at a time  ->  The return value is the bytes read 
    * int read(byte[] b) :  Read one byte array at a time 
    	//byte[] b :  Used to store data read every time 
    int read(byte[] b, int off, int len)  :  Read part of a byte array one at a time 
    
// As long as there is a line break in the file , that read Method can read the newline character