Java File class

Programs may often need to obtain information about files on the disk or create new files on the disk, etc. This requires learning to use the File class . It should be noted that the object of the File class is mainly used to obtain some information about the file itself, such as the directory where the file is located, the length of the file, or file read and write permissions, etc. It does not involve reading and writing operations on the file.

There are three constructors for creating a File object:

1) File(String filename);

2) File(String directoryPath,String filename);

3) File(File dir,String filename);

Among them, filename is the file name, directoryPath is the path of the file, and dir is a directory. When you create a file using File(String filename), the file is considered to be in the same directory as the current application.

Commonly used methods of the File class are as follows:

1) public String getName()

Get the name of the file.

2) public boolean canRead()

Determine whether the file is readable.

3) public boolean canWrite()

Determine whether the file can be written.

4) public boolean exists()

Determine whether the file exists.

5) public long length()

Get the length of the file (unit is bytes).

6) public String getAbsolutePath()

Get the absolute path of the file.

7) public String getParent()

Get the parent directory of the file.

8) public boolean isFile()

Determines whether the file is a regular file, not a directory.

9) public boolean isDirectory()

Determine whether the file is a directory.

10) public boolean isHidden()

Determine whether the file is a hidden file.

11) public long lastModified()

Get the last modified time of the file (the time is the number of milliseconds from midnight 1970 to the last modified time of the file).

For example, create a new file named new.txt:

 importjava.io.*;publicclassMain{publicstaticvoidmain(Stringargs[]){Filef=newFile(C:\ch10,Main.java);System.out.println(f.getName()+Is it readable:+f .canRead());System.out.println(f.getName()+absolute path:+f.getAbsolutePath());Filefile=newFile(new.txt);System.out.println(created in the current directory New file+file.getName());if(!file.exists()){try{file.createNewFile();System.out.println(created successfully);}catch(IOExceptionexp){}}}}

The running results are as follows:

 Is C:ch10>java.MainMain.java readable: The absolute path of trueMain.java: C:ch10Main.java Create a new file new.txt in the current directory and create it successfully