Initial i/o and its basic operations

One 、 File storage structure

File is made up of OS And file system management
1、 The file is in a tree structure （ It's like a binary tree , But not a binary tree ） Conduct management , Files are nodes in the tree （node）
2、 Documents can be divided into two categories ：
1）、 File to store data —— Ordinary documents （ Commonly known as file ）
2）、 Manage files organized in a tree structure —— Catalog / Folder

3、 This tree is just a logical structure , It is not the physical structure on the hard disk （ A file may be a combination of multiple parts on the disk ）

Two 、 Path to file

What is the file path ： The path to the file is , According to a rule , Uniquely identify a location from the file tree , This position must correspond to a node , This node may not exist .

1、 Absolute path

The path described from the root node of a tree
For example, we use absolute path to express hello.jpg file
C：/Windows/Users/hello.jgp

2、 Relative paths

Starting from the current position , Describe the location of the target file
For example, in hello.jpg Location description a.txt The location of
hello.jpg Parent node Users Parent node Windows Parent node C： In the catalog a.txt;

3、 Special symbols for path representation

“.”： Indicates in the current position
“…”： Represents the parent node returning to the current position （ Catalog ） On

3、 ... and 、 Operation of file

In the file system , Operate in node units （ The code level ）
for example ：
File movement ( File rename , File cutting + Paste )： Node movement （ rename or Move to another node ）
File copy operation ： New node + Copy of content
Directory move operation （ Rename the directory 、 Catalog clipping + Paste ）： The movement of a subtree rooted in the node bit
Directory copy operation : Copy of a subtree rooted in the node bit
Delete ： By default, only normal files or non empty directories can be deleted . Only nodes can be deleted , Cannot delete subtree
Delete non empty directory ： Deletion of the entire tree （ You should traverse and delete the leaf node first , Then delete the whole tree ）;

Four 、 utilize Java The code implements the basic operation of the file

1、 Construction method

Create a File object , For this File Object , modify , Delete and other operations

        //1. Create an absolute path 
        File file1 = new File("D:/IO/hello.txt");
        //2. Pass in the parent directory + Subpath 
        File file2 = new File("D:/IO", "hello.txt");
        //3. With File Pass in parent
        File parent = new File("D:/IO");
        File file3 = new File(parent, "hello.txt");

2、 Common methods

Test file permissions

Create a new file

for example

File file=new File("D:/IO/test.txt");
file.createNewFile();// It will be in D:/IO  Create a directory called test Of txt file （ Be careful , If the file already exists in the directory, the creation will fail ）

Delete file

According to the previous example , We created one test.txt file
We can call delete（） Method to delete it

file.delete();// Only leaf nodes can be operated 
// Be careful ： When the file is being used by another thread , Deletion will fail . At the same time, if this file does not exist in the current directory, it will also fail to delete 
// Deleting a non empty directory will also fail 

3、 Delete non empty directory

When deleting a non empty directory , We need to analogy binary tree , You need to delete all its leaf nodes before deleting the whole tree , The following is a method of depth first traversal to delete non empty directories

Delete non empty directory some_dir

    public static void main(String[] args) throws IOException {
    
        File file=new File("D:/IO/some_dir");
        traversal(file);
    }

    /** *  Depth first traverses the child nodes of the current file directory （ Similar to the traversal of binary tree ） * @param file * @throws IOException */
    private static void traversal(File file) throws IOException {
    
        File[] files=file.listFiles();
        for (File file1 : files) {
    
            if (file1.isDirectory()){
    
                System.out.println(file1.getCanonicalPath()+"\\");
                traversal(file1);
                // Add delete operation 
                file1.delete();
            }else {
    
                System.out.println(file1.getCanonicalPath());
                // Add delete operation 
                file1.delete();
            }
        }
    }