[Chapter 11] File

#

| Chapter 11 The java.io Package |

# File

## Name

File

## Synopsis

Class Name:

  `java.io.File`

Superclass:

  `java.lang.Object`

Immediate Subclasses:

  None

Interfaces Implemented:

  None

Availability:

  JDK 1.0 or later

## Description

The `File` class provides methods to obtain information about files and directories. A `File` object encapsulates the name of a file or a directory. A `File` object can list the files in a directory, check the existence and type of a file, create new directories, and rename and delete files, among other things. However, the `File` class does not handle I/O to files. Actual reading and writing is accomplished using `RandomAccessFile`, `FileReader`, `FileWriter`, `FileInputStream`, and `FileOutputStream` objects.

The `File` class also defines some constants for the platform-specific directory and path separator characters. If you want to avoid putting system-dependent path information in your program, you may want to reference all files relative to the directory in which your program is running (i.e., the current directory). Alternatively, you can use `java.awt.FileDialog` to prompt the user for system-dependent paths.

Many of the methods in `File` throw a `SecurityException` if the application does not have sufficient privileges for the requested operation. This happens in two steps. First, `System.getSecurityManager()` is called. If a `SecurityManager` has been installed, it is queried for the appropriate permission. For example, `File.canRead()` calls `SecurityManager.canRead()`. If the application does not have permission to read the specified file, the `SecurityManager` throws a `SecurityException`, which in turn is thrown by `File.canRead()`.

## Class Summary

    public class java.io.File extends java.lang.Object
                              implements java.io.Serializable {
      // Constants
      public final static String pathSeparator;
      public final static char pathSeparatorChar;
      public final static String separator;
      public final static char separatorChar;
      // Constructors
      public File(String path);
      public File(String path, String name);
      public File(File dir, String name);
      // Instance Methods
      public boolean canRead();
      public boolean canWrite();
      public boolean delete();
      public boolean equals(Object obj);
      public boolean exists();
      public String getAbsolutePath();
      public String getCanonicalPath();              // New in 1.1
      public String getName();
      public String getParent();
      public String getPath();
      public int hashCode();
      public native boolean isAbsolute();
      public boolean isDirectory();
      public boolean isFile();
      public long lastModified();
      public long length();
      public String[] list();
      public String[] list(FilenameFilter filter);
      public boolean mkdir();
      public boolean mkdirs();
      public boolean renameTo(File dest);
      public String toString();
    }

## Constants

### pathSeparator

#### public final static String pathSeparator

Description

  This string holds the value of `System.getProperty('path.separator')`. It contains the character that separates paths in a path list. Usually it is "`:`" or "`;`".

### pathSeparatorChar

#### public final static char pathSeparatorChar

Description

  This variable holds the first (and only) character in `pathSeparator`.

### separator

#### public final static String separator

Description

  This string holds the value of `System.getProperty('file.separator')`. It contains the character that separates directory and filenames in a path string. Usually it is "`/`" or "`\`".

### separatorChar

#### public final static char separatorChar

Description

  This variable holds the first (and only) character in `separator`.

## Constructors

### File

#### public File(String path)

Parameters

  `path`

    A full pathname (i.e., a directory and filename).

Description

  This constructor creates a `File` object that represents the file specified by `path`.

#### public File(String path, String name)

Parameters

  `path`

    A directory path.

  `name`

    A filename.

Description

  This constructor creates a `File` object that represents the file with the specified `name` in the directory described by `path`. In other words, the full pathname is the directory, followed by the separator character, followed by the filename.

  If `path` is `null`, the constructor creates a `File` that represents the file with the specified `name` in the current directory. The current directory is the directory in which the program is running.

#### public File(File dir, String name)

Parameters

  `dir`

    A `File` object that represents a directory.

  `name`

    A filename.

Description

  This constructor creates a `File` object that represents the file with the specified `name` in the directory described by the `File` object `dir`. In other words, the full pathname is the directory represented by `dir`, followed by the separator character, followed by the filename.

  If `dir` is `null`, the constructor creates a `File` that represents the file with the specified `name` in the current directory. The current directory is the directory in which the program is running.

## Instance Methods

### canRead

#### public boolean canRead()

Returns

  A `boolean` value that indicates if the file is readable.

Throws

  `SecurityException`

    If the application does not have permission to read the `File`.

Description

  This method returns `true` if `File` corresponds to an existing, readable file or directory. Otherwise it returns `false`.

### canWrite

#### public boolean canWrite()

Returns

  A `boolean` value that indicates if the file is writable.

Throws

  `SecurityException`

    If the application does not have permission to write to the `File`.

Description

  This method returns `true` if `File` corresponds to an existing, writable file or directory. Otherwise it returns `false`.

### delete

#### public boolean delete()

Returns

  `true` if the file is deleted; otherwise `false`.

Throws

  `SecurityException`

    If the application does not have permission to delete the file.

Description

  This method attempts to delete the file or directory associated with this `File` object. A directory is only deleted if it is empty.

### equals

#### public boolean equals(Object obj)

Parameters

  `obj`

    The `Object` to be compared.

Returns

  `true` if the objects are equal; `false` if they are not.

Overrides

  `Object.equals()`

Description

  This method returns `true` if `obj` is an instance of `File` that encapsulates the same pathname as this object.

### exists

#### public boolean exists()

Returns

  `true` if the file or directory exists; `false` otherwise.

Throws

  `SecurityException`

    If the application does not have permission to read the `File`.

Description

  This method returns `true` if this `File` corresponds to an existing file or directory.

### getAbsolutePath

#### public String getAbsolutePath()

Returns

  A `String` that contains the absolute pathname.

Description

  This method returns the absolute pathname of the file or directory associated with this `File`.

### getCanonicalPath

#### public String getCanonicalPath() throws IOException

Availability

  New as of JDK 1.1

Returns

  A `String` that contains the canonical, or exact, pathname.

Throws

  `IOException`

    If any kind of I/O error occurs.

Description

  This method returns the canonical pathname of the file or directory associated with this `File`.

### getName

#### public String getName()

Returns

  A `String` that contains the filename.

Description

  This method returns the filename associated with this`File`. The string returned does not include the name of the directory.

### getParent

#### public String getParent()

Returns

  A `String` that contains the parent directory of the file, or `null` if it does not exist.

Description

  This method returns the name of the parent directory of the file or directory associated with this `File`. The algorithm used returns everything in the pathname before the last separator character.

### getPath

#### public String getPath()

Returns

  A `String` that contains the pathname of the file.

Description

  This method returns the full pathname associated with this `File`.

### hashCode

#### public int hashCode()

Returns

  A hashcode value for this file.

Overrides

  `Object.hashCode()`

Description

  This method returns a hashcode based on the pathname associated with this `File`.

### isAbsolute

#### public native boolean isAbsolute()

Returns

  `true` if the `File` represents an absolute path; `false` otherwise.

Description

  This method indicates if the `File` represents an absolute path; what constitutes an absolute path is system-dependent.

### isDirectory

#### public boolean isDirectory()

Returns

  `true` if the `File` represents a directory; `false` otherwise.

Throws

  `SecurityException`

    If the application does not have permission to read the `File`.

Description

  This method returns `true` if this `File` corresponds to a directory.

### isFile

#### public boolean isFile()

Returns

  `true` if the `File` represents a normal file; `false` otherwise.

Throws

  `SecurityException`

    If the application does not have permission to read the `File`.

Description

  This method returns `true` if this `File` corresponds to a normal file, as opposed to an alternative, such as a directory, a named pipe, or a device.

### lastModified

#### public long lastModified()

Returns

  The time the file was last modified, or `0L` if the file does not exist.

Throws

  `SecurityException`

    If the application does not have permission to read the `File`.

Description

  This method returns the modification time of the file or directory that corresponds to this `File`. The format of the time returned is useful for comparing modification times; it's not meant to be used for other purposes.

### length

#### public long length()

Returns

  The file length, in bytes, or `0L` if the file does not exist.

Throws

  `SecurityException`

    If the application does not have permission to read the `File`.

Description

  This method returns the length of the file or directory that corresponds to this `File`.

### list

#### public String[] list()

Returns

  An array of the names of the files and directories contained by this `File`, or `null` if this `File` is not a directory.

Throws

  `SecurityException`

    If the application does not have permission to read the `File`.

Description

  This method returns the contents of a directory. The current directory and the parent directory are not included in the list.

#### public String[] list(FilenameFilter filter)

Parameters

  `filter`

    A filter to use.

Returns

  An array of the names of the files and directories contained by this `File` and filtered by `filter`, or `null` if this `File` is not a directory.

Throws

  `SecurityException`

    If the application does not have permission to read the `File`.

Description

  This method returns of the contents of a directory as selected by the given `FilenameFilter` object. Specifically, a name is included if the `FilenameFilter` object's `accept()` method returns `true` for that name.

  If `filter` is `null`, this method is equivalent to, but slower than, `list()`.

### mkdir

#### public boolean mkdir()

Returns

  `true` if the directory is created; `false` otherwise.

Throws

  `SecurityException`

    If the application does not have permission to write to the `File`.

Description

  This method creates a directory with the pathname specified by this `File`.

### mkdirs

#### public boolean mkdirs()

Returns

  `true` if the directory is created; `false` otherwise.

Throws

  `SecurityException`

    If the application does not have permission to write to the `File`.

Description

  This method creates a directory with the pathname specified by this `File`. The method also creates all the parent directories if necessary.

### renameTo

#### public boolean renameTo(File dest)

Parameters

  `dest`

    A `File` that specifies the new name.

Returns

  `true` if the name is changed; `false` otherwise.

Throws

  `SecurityException`

    If the application does not have permission to write to this `File` or the file represented by `dest`.

Description

  This method changes the pathname of this `File` to the pathname specified by `dest`.

### toString

#### public String toString()

Returns

  A `String` that contains the pathname of this `File`.

Overrides

  `Object.toString()`

Description

  This method returns a string representation of this `File` object.

## Inherited Methods

Method | Inherited From | Method | Inherited From
--- | --- | --- | ---
`clone()` | `Object` | `finalize()` | `Object`
`getClass()` | `Object` | `notify()` | `Object`
`notifyAll()` | `Object` | `wait()` | `Object`
`wait(long)` | `Object` | `wait(long, int)` | `Object`

## See Also

`FileInputStream`, `FilenameFilter`, `FileOutputStream`, `FileReader`, `FileWriter`, `IOException`, `SecurityException`

Externalizable |  | FileDescriptor