IO stream (file class introduction)

One 、FiLe The use of the class

1. File An object of class , Represents a file or a file directory ( Be commonly called : Folder )
2. File Class declaration in java.io It's a bag 
3. File Class involves the creation of files or file directories 、 Delete 、 rename 、 Modification time 、 File size, etc ,
    It does not involve writing or reading the contents of the file . If you need to read or write the contents of the file , You have to use Io Flow to complete .
4. explain :
 IDEA in :
  If unit test method is used to test , The relative path is the current Module Next .
  If you use main() test , The relative path is the current Project Next .
 Eclipse in :
  Whether using unit testing methods or using main() test , Relative paths are all current Project Next .

establish File Class instance 、 Introduce File Methods defined in class ：

1. How to create FiLe Class 
  new File(String filepath)
  File(string parentPath,String childPath)
  File(File parentFile,string childPath)
2. Relative paths : Compared with a certain path , The path indicated .
   Absolute path : The path to the file or file directory that contains the drive letter 
3. Separator 
  windows：\\
  Unix：/
   Universal ：File.separator

public void test1() {
//         Creation method 1 ：
        File file1 = new File("hello.txt");
        File file2 = new File("D:\\software\\idea\\project\\day08");
//         Creation mode 2 ：
        File file3 = new File("D:\\software", "idea\\project");
//         Creation method 3 ：
        File project = new File(file3, "hi.txt");
    }

 

public String getAbsoLutePath(): Get absolute path pablic string getPath() : Get path 
public string getName() : Get the name 
public string getParent(): Get the upper file directory path . If there is no , return nuLL
public long length() : Get file length ( namely : Number of bytes ）. Cannot get the length of the directory .
public long LastModified() : Get the last modification time , Millisecond value 
 The following two methods apply to the file directory 
public string[] list() : Get the name array of all files or file directories in the specified directory 
public File[] listFiles() : Get all the files in the specified directory or file directory FiLe Array 

public boolean renameTo(File dest): Rename the file to the specified file path 
 With file1.renameTo（file2） For example ：
 To return to true, requirement file1 There must be ,file2 Can't exist 

 public void test3(){
        File file1 = new File("hello");// Here my file name is hello, Can not write hello.txt
        File file2 = new File("D:\\io\\hi.txt");
        boolean b = file1.renameTo(file2);
        System.out.println(b);
    }

public booLean isDirectory(): Determine whether it is a file directory 
public boolean isFile() : Determine if it's a document 
public booLean exists() : Judge whether it exists           This is usually used first to judge whether it is in 
public boolean canRead() : Judge whether it is readable 
public boolean canwrite() : Judge whether it is writable 
public boolean isHidden() : Determine whether to hide 

 Create the corresponding file or file directory in the hard disk 
public boolean createNewFile() : create a file . If the file exists , Do not create , return false
public boolean mkdir() :  Create file directory . If this file directory exists , We won't create . If the upper directory of this file directory does not exist , It doesn't create .
public boolean mkdirs() : Create file directory . If the upper file directory does not exist , Create... Together 

 Delete a file or file directory from the disk 
public boolean delete(): Delete files or folders 
 Delete notes :
Java Delete in does not go to the recycle bin .