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public class  Relative paths  {
    public static void main(String[] args) throws IOException {
        File file = new File("./a.txt");
        System.out.println(file.getCanonicalPath());
    }
}

The current in file Folder ： describe a.txt for ： file\a.txt

Path in code : windows in \ To signify an escape , therefore windows Code in ： D:\\file\\a.txt

java Is a cross platform language , So the code can not distinguish between forward and backward slashes

File class ：

Construction method

Common method ：

Delete file delete()

Only leaf nodes or empty folders can be deleted ;

deleteOnExit() ： Delete files when program exits ;

Delete non empty folder , You can only delete the folder as empty , To delete the folder

Document creation and judgment

windows Deleting files on is equivalent to cutting and copying , Copy files from the current node to the recycle bin ,

delete() The method is to delete the real file system , Don't go into the recycle bin

package com.yyk.io.IO Operation file ;

import java.io.File;
import java.io.IOException;
import java.util.ArrayDeque;
import java.util.Arrays;
import java.util.Date;
import java.util.Deque;

public class FileMetohd {
    public static void main(String[] args) throws IOException {
        File file = new File("D:\\IO\\.\\..\\..\\IO\\hello.txt");
        System.out.println(" Does the file exist ："+file.exists());
        System.out.println(" Is it a folder ："+file.isDirectory());
        System.out.println(" Is it a document " + file.isFile());
        System.out.println("*********** Create... Under this path hello.txt*******");
        file.createNewFile();
        System.out.println(" Does the file exist ："+file.exists());
        System.out.println(" Is it a folder ："+file.isDirectory());
        System.out.println(" Is it a document " + file.isFile());
        System.out.println();
        System.out.println("******** Get the path of the file **********");
        System.out.println(" The absolute path of the file ：" +file.getAbsoluteFile());// The returned file 
        System.out.println(" The absolute path of the file ：" +file.getAbsolutePath());// Return a string 
        System.out.println(" The authoritative absolute path of the file ：" +file.getCanonicalFile());// The returned file , Remove the meaningless point in the middle 
        System.out.println(" The authoritative absolute path of the file ：" +file.getCanonicalPath());// Return a string , Remove the middle file .. and .
        System.out.println(" file name ：" + file.getName());
        System.out.println(" The parent path of the file ：" + file.getParent());
        System.out.println(" Authoritative path of the parent path of the file ：" + file.getParentFile().getCanonicalPath());
        System.out.println(" File size ：" + file.length());
        System.out.println(" Files created with absolute paths ：" +file.isAbsolute());
        System.out.println(" Is the file hidden ：" +file.isHidden());
        System.out.println(" The last time the file was modified ：" + new Date(file.lastModified()));
        System.out.println(" The number of files in the parent directory of the file ：" + Arrays.toString(file.getParentFile().listFiles()));
        System.out.println();
        System.out.println("******** The depth of the file is traversed first ***********");
        DFSFilePath(file.getParentFile());
        System.out.println();
        System.out.println("******** Breadth first traversal of files ***********");
        NFSFilePath(file.getParentFile());
        System.out.println(" The root directory of the file system " + file.listRoots());
        System.out.println();
        System.out.println("*****mkdir**** Create folder *******mkdirs****");
        File file1 = new File("D:\\IO\\A\\BB\\CCC");
        file1.mkdirs();
        System.out.println("mkdirs Create a folder under a nonexistent path " + file1.getCanonicalPath());
        File file2 = new File("D:\\IO\\D");
        file2.mkdir();
        System.out.println("mkdir Create a folder under an existing directory ：" + file2.getCanonicalPath());
        System.out.println(" Rename file :" );
        File dest = new File("D:\\IO\\ Hello .txt");
        System.out.print(file.getName()+"  It was renamed  ");
        file.renameTo(dest);
        dest.delete();// Delete folder 
        System.out.println(dest.getName());
        System.out.println(" Renaming a file is equivalent to cutting and copying a file ");

    }

    /**
     *  The depth of the file is traversed first 
     * @param dir
     */
    public static void DFSFilePath(File dir) throws IOException {
        File[] files = dir.listFiles();
        if (dir == null){
            return;
        }
        for (File file: files) {
            if (file.isDirectory()){
                System.out.println(dir.getCanonicalPath()+" In the catalog "+file.getName()+" Folder ");
                DFSFilePath(file);
            }else {
                System.out.println(dir.getCanonicalPath()+" In the catalog "+file.getName()+" file ");
            }
        }

    }

    /**
     *  File breadth first traversal 
     * @param dir
     * @throws IOException
     */
    public static void NFSFilePath(File dir) throws IOException {
        Deque<File> fileDeque = new ArrayDeque<>();
        fileDeque.offer(dir);
        while (!fileDeque.isEmpty()){
            File file = fileDeque.poll();
            if (file.isDirectory()){
                File[] files = file.listFiles();
                for (File f:files) {
                    fileDeque.offer(f);
                }
                System.out.println(" Folder ：" + file.getCanonicalPath());
            }else {
                System.out.println(" file ：" + file.getCanonicalPath());
            }

        }

    }
}

Reading and writing of documents

Read data of file ：FileInputStream

1, Read the file in the form of byte stream

conceptual model ：

2, Read files in character stream （ Text files ）

Whether it's a byte stream or a character stream , It's all used Scanner Class to read data

public class  Read data with Scanner {
    public static void main(String[] args) throws Exception{
        try(InputStream is = new FileInputStream("./hello.txt")){
            try(Scanner scanner = new Scanner(is,"UTF-8")){
                while (scanner.hasNextLine()){
                    String next = scanner.nextLine();
                    System.out.println(next);
                }
            }
        }
    }
}

Write OutputStream:

Write data when closing resources , You need to flush the buffer , Avoid data that has not been written in the buffer .

Copy of documents

public class  File replication  {
    public static void main(String[] args) throws Exception {
        InputStream is = new FileInputStream("D:\\IO\\12.jpg");
        byte[] buff = new byte[10240];// buffer , Used to match the reading and writing speed gap between memory and hard disk 
        OutputStream os = new FileOutputStream("D:\\IO\\34.jpg");
        while (true){
            int read = is.read(buff);
            if (read == -1){// If it is EOS, There is no data , immediate withdrawal 
                break;
            }
            os.write(buff);// Write all the bytes read into the buffer into the file 
            os.flush();// Finally, flush the buffer zone 
        }

    }
}

Copy of folder

package com.yyk.io.IO Operation file ;

import java.io.*;

public class  Folder copy  {
    static File srcFile = new File("D:\\IO\\A");// Source directory 
    static File tarFile = new File("D:\\IO\\D"); // Destination file directory 
    public static void main(String[] args) throws Exception{
        copy(srcFile);
    }
    private static void copy(File dirFile) throws Exception {
        File[] files = dirFile.listFiles();
        if (files == null){
            return;
        }
        for (File file:files) {
            String filePath = file.getCanonicalPath();// The directory of the current file 
            String tarFilePath = tarFile.getCanonicalPath();// The root directory of the files to be copied 
            String aimPath= tarFilePath + filePath.substring(srcFile.getCanonicalPath().length());// The directory that needs to be copied 
            File aimFile = new File(aimPath);
            if (file.isDirectory()) {// If it's a folder , Create folder 
                aimFile.mkdir();
                // Just continue to traverse 
                copy(file);
            }else if (file.isFile()){
                copyFile(file,aimFile);
            }
        }
    }
    public static void copyFile(File file,File aimFile) throws Exception {
        InputStream is = new FileInputStream(file);
        byte[] buff = new byte[10240];// buffer , Used to match the reading and writing speed gap between memory and hard disk 
        OutputStream os = new FileOutputStream(aimFile);
        while (true){
            int read = is.read(buff);
//            System.out.println(" I read "+read+" Bytes ");
            if (read == -1){// If it is EOS, There is no data , immediate withdrawal 
                break;
            }
            os.write(buff,0,read);// Write all the bytes read into the buffer into the file 
            os.flush();// Finally, flush the buffer zone 
        }

    }
}

simulation OJ Writing of test documents

package com.yyk.io.IO Operation file .oj;

public class Node {
    int val ;
    Node next;
    public Node(int val){
        this.val = val;
    }
}

package com.yyk.io.IO Operation file .oj;

public class Solution {
    public Node reverse(Node head){
        Node prev = null;
        Node cur = head;
        while (cur != null){
            Node next = cur.next;
            cur.next = prev;
            prev = cur;
            cur =next;
        }
        return prev;
    }
}

package com.yyk.io.IO Operation file .oj;

import java.io.File;
import java.io.FileInputStream;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.Scanner;

public class  Test case verification  {
    static Solution solution = new Solution();
    static File inputFile = new File("D:\\IO\\C\\input.txt");
    static File resFile = new File("D:\\IO\\C\\output.txt");

    public static void main(String[] args){
        try{
            // Read input and output files by line 
            InputStream is = new FileInputStream(inputFile);// Input 
            InputStream res = new FileInputStream(resFile);// result 
            Scanner isSc = new Scanner(is,"UTF-8");
            Scanner resSc = new Scanner(res,"UTF-8");
            while (isSc.hasNextLine()){
                String inStr = isSc.nextLine();
                String resStr = resSc.nextLine();
                test(inStr,resStr);
            }
            System.out.println(" Through all the test cases ");
        }catch (Exception e){

        }
    }
    private static void test(String inStr,String resStr){
        StringBuilder sb = new StringBuilder();
        try {
            // take instr Press find space to separate , To int, Create a linked list and reverse 
            String[] strs = inStr.split(" ");
            Node head = new Node(-1);
            Node tem = head;
            for (String s:strs) {
                Node node = new Node(Integer.parseInt(s));
                tem.next = node;
                tem = node;
            }
            Node newNode = solution.reverse(head.next);// New linked list after inversion 
            // Traverse the linked list into a string 
            while (newNode != null){
                sb.append(newNode.val + " ");
                newNode = newNode.next;
            }
            // Finally, remove the last space 
            sb.delete(sb.length() - 1,sb.length());
            if (!resStr.equals(sb.toString())){
                System.out.println(" Enter the use case ：" + inStr);
                System.out.println(" Expected output ：" + resStr);
                System.out.println(" The actual output ：" + sb.toString());
                System.exit(1);
            }
        }catch (Exception e){
            System.out.println(" Enter the use case ：" + inStr);
            System.out.println(" Expected output ：" + resStr);
            System.out.println(" The actual output ：" + sb.toString());
            e.printStackTrace();
        }
    }
}

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当前位置：网站首页>IO should know and should know

IO should know and should know

Hardware architecture ： processor CPU, Memory （ Memory ）, input device , Output devices

Comparison of reading and writing speed of various hardware

File path ： From the file system tree , Find the only certain location , This node may not exist .

Absolute path ： Start from the root node of the file tree , Find the node location of a file , It's the absolute path

Relative paths ： Start from the current file node , The position of the other node relative to the current node