File Management in Java (java.io.File)

Java File class represents the files and directory pathnames in an abstract manner. This class is used for creation of files and directories, file searching, file deletion etc.

The File object represents the actual file/directory on the disk. There are following constructors to create a File object:

Some important operations on File Object are listed here

1. Instantiating a java.io.File

Before you can do anything with the file system or File class, you must obtain a File instance. Here is how that is done: 

File file = new File("c:\\data\\input-file.txt");

Simple, right? The File class also has a few other constructors you can use to instantiate Fileinstances in different ways. 

2. Check if File Exists

Once you have instantiated a File object you can check if the corresponding file actually exists already. The File class constructor will not fail if the file does not already exists. You might want to create it now, right? 
To check if the file exists, call the exists() method. Here is a simple example: 

File file = new File("c:\\data\\input-file.txt");

boolean fileExists = file.exists();

3. File Length

To read the length of a file in bytes, call the length() method. Here is a simple example: 

File file = new File("c:\\data\\input-file.txt");

long length = file.length();

4. Rename or Move File

To rename (or move) a file, call the method renameTo() on the File class. Here is a simple example: 

File file = new File("c:\\data\\input-file.txt");

boolean success = file.renameTo(new File("c:\\data\\new-file.txt"));

5. Delete File

To delete a file call the delete() method. Here is a simple example: 

File file = new File("c:\\data\\input-file.txt");

boolean success = file.delete();

The delete() method returns boolean (true or false), indicating whether the deletion was successful. Deleting a file may fail for various reasons, like the file being open, wrong file permissions etc. 

6. Check if Path is File or Directory

A File object can point to both a file or a directory. 
You can check if a File object points to a file or directory, by calling its isDirectory() method. This method returns true if the File points to a directory, and false if the File points to a file. Here is a simple example: 

File file = new File("c:\\data");

boolean isDirectory = file.isDirectory();

7. Read List of Files in Directory

You can obtain a list of all the files in a directory by calling either the list() method or thelistFiles() method. The list() method returns an array of String's with the file and / or directory names of directory the File object points to. The listFiles() returns an array of File objects representing the files and / or directories in the directory the File points to. 
Here is a simple example: 

File file = new File("c:\\data");

String[] fileNames = file.list();

File[]   files = file.listFiles();

 

 All Methods of File class 

(Do not mug up all the method names. Just try to remember those which are used in programs)

1	public String getName() Returns the name of the file or directory denoted by this abstract pathname.
2	public String getParent() Returns the pathname string of this abstract pathname's parent, or null if this pathname does not name a parent directory.
3	public File getParentFile() Returns the abstract pathname of this abstract pathname's parent, or null if this pathname does not name a parent directory.
4	public String getPath() Converts this abstract pathname into a pathname string.
5	public boolean isAbsolute() Tests whether this abstract pathname is absolute. Returns true if this abstract pathname is absolute, false otherwise
6	public String getAbsolutePath() Returns the absolute pathname string of this abstract pathname.
7	public boolean canRead() Tests whether the application can read the file denoted by this abstract pathname. Returns true if and only if the file specified by this abstract pathname exists and can be read by the application; false otherwise.
8	public boolean canWrite() Tests whether the application can modify to the file denoted by this abstract pathname. Returns true if and only if the file system actually contains a file denoted by this abstract pathname and the application is allowed to write to the file; false otherwise.
9	public boolean exists() Tests whether the file or directory denoted by this abstract pathname exists. Returns true if and only if the file or directory denoted by this abstract pathname exists; false otherwise
10	public boolean isDirectory() Tests whether the file denoted by this abstract pathname is a directory. Returns true if and only if the file denoted by this abstract pathname exists and is a directory; false otherwise.
11	public boolean isFile() Tests whether the file denoted by this abstract pathname is a normal file. A file is normal if it is not a directory and, in addition, satisfies other system-dependent criteria. Any non-directory file created by a Java application is guaranteed to be a normal file. Returns true if and only if the file denoted by this abstract pathname exists and is a normal file; false otherwise
12	public long lastModified() Returns the time that the file denoted by this abstract pathname was last modified. Returns a long value representing the time the file was last modified, measured in milliseconds since the epoch (00:00:00 GMT, January 1, 1970), or 0L if the file does not exist or if an I/O error occurs.
13	public long length() Returns the length of the file denoted by this abstract pathname. The return value is unspecified if this pathname denotes a directory.
14	public boolean createNewFile() throws IOException Atomically creates a new, empty file named by this abstract pathname if and only if a file with this name does not yet exist. Returns true if the named file does not exist and was successfully created; false if the named file already exists.
15	public boolean delete() Deletes the file or directory denoted by this abstract pathname. If this pathname denotes a directory, then the directory must be empty in order to be deleted. Returns true if and only if the file or directory is successfully deleted; false otherwise.
16	public void deleteOnExit() Requests that the file or directory denoted by this abstract pathname be deleted when the virtual machine terminates.
17	public String[] list() Returns an array of strings naming the files and directories in the directory denoted by this abstract pathname.
18	public String[] list(FilenameFilter filter) Returns an array of strings naming the files and directories in the directory denoted by this abstract pathname that satisfy the specified filter.
20	public File[] listFiles() Returns an array of abstract pathnames denoting the files in the directory denoted by this abstract pathname.
21	public File[] listFiles(FileFilter filter) Returns an array of abstract pathnames denoting the files and directories in the directory denoted by this abstract pathname that satisfy the specified filter.
22	public boolean mkdir() Creates the directory named by this abstract pathname. Returns true if and only if the directory was created; false otherwise
23	public boolean mkdirs() Creates the directory named by this abstract pathname, including any necessary but nonexistent parent directories. Returns true if and only if the directory was created, along with all necessary parent directories; false otherwise.
24	public boolean renameTo(File dest) Renames the file denoted by this abstract pathname. Returns true if and only if the renaming succeeded; false otherwise
25	public boolean setLastModified(long time) Sets the last-modified time of the file or directory named by this abstract pathname. Returns true if and only if the operation succeeded; false otherwise .
26	public boolean setReadOnly() Marks the file or directory named by this abstract pathname so that only read operations are allowed. Returns true if and only if the operation succeeded; false otherwise.