I/O Flow principle and classification of flow

I/O principle

• I/O yes Input and Output Abbreviation ,I/O Technology is a very practical technology , Used to handle data transmission （ Such as ： read / Writing documents , Network communication ）
• Java In the program , For data input / The output operation is based on flow (stream) In the way of
• java.io A variety of flow (stream) Classes and interfaces , To get different kinds of data , And input and output data through methods .
• File stream ： Files are operated in the form of stream in the program

Input stream ： Data from data sources （ file ） To the program （ Memory ） The path of
Output stream ： Data from the program （ Memory ） To the data source （ file ） The path of

I/O Classification of flows

• It is divided into... According to the unit of operation data ： Byte stream （ Binary ）、 Character stream （ text file ）
• It is divided into... According to the flow direction of data ： Input stream 、 Output stream
• According to the role of flow, it is divided into ： Node flow 、 Processing flow

Abstract base class	Byte stream	Character stream
Input stream	InputStream	Reader
Output stream	OutputStream	Writer

️I/O Architecture of

️ file （File）

Concept

• What is a document ？

file , It's not new to us , A file is where data is stored , such as word file 、txt Text 、excel file 、 picture 、 video … It's all documents , In the operating system, the data in the disk is managed in the unit of file . From a data storage perspective , All documents are essentially the same , They are all composed of bytes. In the final analysis, they are 0-1 Bit string .

• Folder （ Catalog ）

If multiple files are not classified and put together , It is very inconvenient for users to use , therefore , A tree directory is also introduced （ It's also called a folder ） The mechanism of , You can put files in different folders , Folders can also be nested in folders , This makes it easy for users to manage and use files .

️ Common operations （File class ）

• Create file object related constructors and methods

new File(String pathname);// Build a... Based on the path File object
new File(File parent,String child);// According to the parent directory file + Sub path construction
new File(String parent,String child);// According to the parent directory path + Sub path construction
createNewFile();// Create a new file

stay E Under the plate , Create the file in the above way test01.txt\test02.txt\test03.txt

import java.io.File;
import java.io.IOException;

public class FileCreate {
    
    public static void main(String[] args) throws IOException {
    
        // The way 1
        String pathname = "e:\\test01.txt";
        File file1 = new File(pathname);
        file1.createNewFile();
        // The way 2
        File parentfile = new File("e:\\");
        String child2 = "test02.txt";
        File file2 = new File(parentfile, child2);
        file2.createNewFile();
        // The way 3
        String parent = "e:\\";
        String child3 = "test03.txt";
        File file3 = new File(parent, child3);
        file3.createNewFile();
    }
}

• Get information about the file

get.getName();// Get the file name

canRead();// Is the file readable

canWrite();// Is the document writable

getAbsoultePath();// Get the absolute path of the file

getPath();// Relative paths

getParent();// Get file parent directory

lenth();// file size （ byte ）

exists();// Judge whether the file exists

isFile();// Judge whether it's a file

isDirectory();// Determine whether it is a directory

import java.io.File;

public class FileInfomation {
    
    public static void main(String[] args) {
    
        // Create a file object 
        File file = new File("e:\\test01.txt");
        System.out.println(" File name ：" + file.getName());
        System.out.println(" Is the file readable ：" + file.canRead());
        System.out.println(" Is the document writable ：" + file.canWrite());
        System.out.println(" File absolute path ：" + file.getAbsolutePath());
        System.out.println(" file size （ byte ）：" + file.length());
        System.out.println(" Does the file exist ：" + file.exists());
        System.out.println(" Is it a file ：" + file.isFile());
        System.out.println(" Is it a directory ：" + file.isDirectory());
    }
}

• The file is

File f1=new File("D:\\test1.txt");
File f2=new File("D:\\test2.txt");
f1==f2;// Compare the addresses of the two objects 
f1.equals(f2);// Compare the path of the file corresponding to the two objects 

• Directory operation and file deletion

mkdir();// Create a single level directory

mkdirs();// Create a multi-level catalog

delete();// Delete directory （ This layer directory must be empty , No content ）

• Check the file directory

list();// Returns an array of strings , Name the files and directories in the directory represented by this abstract pathname .

listFiles();// Returns an array of abstract pathnames , Represents the files in the directory represented by the abstract pathname .

Case list : Traverse all files in a directory and print out

public class PrintFile {
    
    public static void main(String[] args) {
    
        // Create a file object 
        File file = new File("e:\\Test");
        String[] list = file.list();// Directory under folder / An array of names corresponding to the file 
        for (String s : list) {
    
            System.out.println(s);
        }
        File[] files = file.listFiles();
        for (File f : files) {
    
            System.out.println(f.getName() + "," + f.getAbsolutePath());
        }
    }
}

Traverse the directory

1. Given a file object file
2.listFiles() Get the array of all file objects under the file
3. Traverse File An array of objects , If it's a catalog , Recursively call this method to get all file objects in this directory ; If it's a file , Printout path + full name

import java.io.File;

public class PrintFile {
    
    public static void main(String[] args) {
    
        File file = new File("E:\\Code");
        getAllFile(file);
    }

    public static void getAllFile(File file) {
    
        // Get all the files in the given directory File An array of objects 
        File[] files = file.listFiles();
        // To traverse the 
        if (files != null) {
    
            for (File f : files) {
    
                if (f.isDirectory()) {
    // Determine whether it is a directory , If it is , Call recursion 
                    getAllFile(f);
                } else {
    // No , Print path + file name 
                    System.out.println(f.getAbsoluteFile() + " Under the ：" + f.getName());
                }
            }
        }
    }
}