public class File extends Object implements Serializable, Comparable<File>
The actual file referenced by a File
may or may not exist. It may
also, despite the name File
, be a directory or other non-regular
file.
This class provides limited functionality for getting/setting file permissions, file type, and last modified time.
On Android strings are converted to UTF-8 byte sequences when sending filenames to
the operating system, and byte sequences returned by the operating system (from the
various list
methods) are converted to strings by decoding them as UTF-8
byte sequences.
Serializable
,
Comparable
,
Serialized FormModifier and Type | Field and Description |
---|---|
static String |
pathSeparator
The system-dependent string used to separate components in search paths (":").
|
static char |
pathSeparatorChar
The system-dependent character used to separate components in search paths (':').
|
static String |
separator
The system-dependent string used to separate components in filenames ('/').
|
static char |
separatorChar
The system-dependent character used to separate components in filenames ('/').
|
Constructor and Description |
---|
File(File dir,
String name)
Constructs a new file using the specified directory and name.
|
File(String path)
Constructs a new file using the specified path.
|
File(String dirPath,
String name)
Constructs a new File using the specified directory path and file name,
placing a path separator between the two.
|
File(URI uri)
Constructs a new File using the path of the specified URI.
|
Modifier and Type | Method and Description |
---|---|
boolean |
canExecute()
Tests whether or not this process is allowed to execute this file.
|
boolean |
canRead()
Indicates whether the current context is allowed to read from this file.
|
boolean |
canWrite()
Indicates whether the current context is allowed to write to this file.
|
int |
compareTo(File another)
Returns the relative sort ordering of the paths for this file and the
file
another . |
boolean |
createNewFile()
Creates a new, empty file on the file system according to the path
information stored in this file.
|
static File |
createTempFile(String prefix,
String suffix)
Creates an empty temporary file using the given prefix and suffix as part
of the file name.
|
static File |
createTempFile(String prefix,
String suffix,
File directory)
Creates an empty temporary file in the given directory using the given
prefix and suffix as part of the file name.
|
boolean |
delete()
Deletes this file.
|
void |
deleteOnExit()
Schedules this file to be automatically deleted when the VM terminates normally.
|
boolean |
equals(Object obj)
Compares
obj to this file and returns true if they
represent the same object using a path specific comparison. |
boolean |
exists()
Returns a boolean indicating whether this file can be found on the
underlying file system.
|
File |
getAbsoluteFile()
Returns a new file constructed using the absolute path of this file.
|
String |
getAbsolutePath()
Returns the absolute path of this file.
|
File |
getCanonicalFile()
Returns a new file created using the canonical path of this file.
|
String |
getCanonicalPath()
Returns the canonical path of this file.
|
long |
getFreeSpace()
Returns the number of free bytes on the partition containing this path.
|
String |
getName()
Returns the name of the file or directory represented by this file.
|
String |
getParent()
Returns the pathname of the parent of this file.
|
File |
getParentFile()
Returns a new file made from the pathname of the parent of this file.
|
String |
getPath()
Returns the path of this file.
|
long |
getTotalSpace()
Returns the total size in bytes of the partition containing this path.
|
long |
getUsableSpace()
Returns the number of usable free bytes on the partition containing this path.
|
int |
hashCode()
Returns an integer hash code for the receiver.
|
boolean |
isAbsolute()
Indicates if this file's pathname is absolute.
|
boolean |
isDirectory()
Indicates if this file represents a directory on the
underlying file system.
|
boolean |
isFile()
Indicates if this file represents a file on the underlying
file system.
|
boolean |
isHidden()
Returns whether or not this file is a hidden file as defined by the
operating system.
|
long |
lastModified()
Returns the time when this file was last modified, measured in
milliseconds since January 1st, 1970, midnight.
|
long |
length()
Returns the length of this file in bytes.
|
String[] |
list()
Returns an array of strings with the file names in the directory
represented by this file.
|
String[] |
list(FilenameFilter filter)
Gets a list of the files in the directory represented by this file.
|
File[] |
listFiles()
Returns an array of files contained in the directory represented by this
file.
|
File[] |
listFiles(FileFilter filter)
Gets a list of the files in the directory represented by this file.
|
File[] |
listFiles(FilenameFilter filter)
Gets a list of the files in the directory represented by this file.
|
static File[] |
listRoots()
Returns the file system roots.
|
boolean |
mkdir()
Creates the directory named by this file, assuming its parents exist.
|
boolean |
mkdirs()
Creates the directory named by this file, creating missing parent
directories if necessary.
|
boolean |
renameTo(File newPath)
Renames this file to
newPath . |
boolean |
setExecutable(boolean executable)
Equivalent to setExecutable(executable, true).
|
boolean |
setExecutable(boolean executable,
boolean ownerOnly)
Manipulates the execute permissions for the abstract path designated by
this file.
|
boolean |
setLastModified(long time)
Sets the time this file was last modified, measured in milliseconds since
January 1st, 1970, midnight.
|
boolean |
setReadable(boolean readable)
Equivalent to setReadable(readable, true).
|
boolean |
setReadable(boolean readable,
boolean ownerOnly)
Manipulates the read permissions for the abstract path designated by this
file.
|
boolean |
setReadOnly()
Equivalent to setWritable(false, false).
|
boolean |
setWritable(boolean writable)
Equivalent to setWritable(writable, true).
|
boolean |
setWritable(boolean writable,
boolean ownerOnly)
Manipulates the write permissions for the abstract path designated by this
file.
|
String |
toString()
Returns a string containing a concise, human-readable description of this
file.
|
URI |
toURI()
Returns a Uniform Resource Identifier for this file.
|
URL |
toURL()
Deprecated.
use
toURI() and URI.toURL() to get
correct escaping of illegal characters. |
public static final char separatorChar
This field is initialized from the system property "file.separator". Later changes to that property will have no effect on this field or this class.
public static final String separator
separatorChar
.public static final char pathSeparatorChar
This field is initialized from the system property "path.separator". Later changes to that property will have no effect on this field or this class.
public static final String pathSeparator
pathSeparatorChar
.public File(File dir, String name)
dir
- the directory where the file is stored.name
- the file's name.NullPointerException
- if name
is null
.public File(String path)
path
- the path to be used for the file.public File(String dirPath, String name)
dirPath
- the path to the directory where the file is stored.name
- the file's name.NullPointerException
- if name == null
.public File(URI uri)
uri
needs to be an absolute and hierarchical Unified Resource Identifier with
file scheme and non-empty path component, but with undefined authority,
query or fragment components.uri
- the Unified Resource Identifier that is used to construct this
file.IllegalArgumentException
- if uri
does not comply with the conditions above.toURI()
,
URI
public static File[] listRoots()
/
.public boolean canExecute()
true
if this file can be executed, false
otherwise.public boolean canRead()
true
if this file can be read, false
otherwise.public boolean canWrite()
true
if this file can be written, false
otherwise.public int compareTo(File another)
another
. The ordering is platform dependent.compareTo
in interface Comparable<File>
another
- a file to compare this file toComparable
public boolean delete()
Note that this method does not throw IOException
on failure.
Callers must check the return value.
true
if this file was deleted, false
otherwise.public void deleteOnExit()
Note that on Android, the application lifecycle does not include VM termination, so calling this method will not ensure that files are deleted. Instead, you should use the most appropriate out of:
finally
clause to manually invoke delete()
.
public boolean equals(Object obj)
obj
to this file and returns true
if they
represent the same object using a path specific comparison.equals
in class Object
obj
- the object to compare this file with.true
if obj
is the same as this object,
false
otherwise.Object.hashCode()
public boolean exists()
true
if this file exists, false
otherwise.public String getAbsolutePath()
/
.
A common use for absolute paths is when passing paths to a Process
as
command-line arguments, to remove the requirement implied by relative paths, that the
child must have the same working directory as its parent.
public File getAbsoluteFile()
new File(this.getAbsolutePath())
.public String getCanonicalPath() throws IOException
Most callers should use getAbsolutePath()
instead. A canonical path is
significantly more expensive to compute, and not generally useful. The primary
use for canonical paths is determining whether two paths point to the same file by
comparing the canonicalized paths.
It can be actively harmful to use a canonical path, specifically because canonicalization removes symbolic links. It's wise to assume that a symbolic link is present for a reason, and that that reason is because the link may need to change. Canonicalization removes this layer of indirection. Good code should generally avoid caching canonical paths.
IOException
- if an I/O error occurs.public File getCanonicalFile() throws IOException
new File(this.getCanonicalPath())
.IOException
- if an I/O error occurs.public String getName()
public String getParent()
null
is returned if there is no
parent.null
.public File getParentFile()
null
is
returned when there is no parent.null
.public String getPath()
public int hashCode()
equals
returns true
must return the same hash code.hashCode
in class Object
equals(java.lang.Object)
public boolean isAbsolute()
true
if this file's pathname is absolute, false
otherwise.getPath()
public boolean isDirectory()
true
if this file is a directory, false
otherwise.public boolean isFile()
true
if this file is a file, false
otherwise.public boolean isHidden()
true
if the file is hidden, false
otherwise.public long lastModified()
public boolean setLastModified(long time)
Note that this method does not throw IOException
on failure.
Callers must check the return value.
time
- the last modification time for this file.true
if the operation is successful, false
otherwise.IllegalArgumentException
- if time < 0
.public boolean setReadOnly()
setWritable(boolean, boolean)
public boolean setExecutable(boolean executable, boolean ownerOnly)
Note that this method does not throw IOException
on failure.
Callers must check the return value.
executable
- To allow execute permission if true, otherwise disallowownerOnly
- To manipulate execute permission only for owner if true,
otherwise for everyone. The manipulation will apply to
everyone regardless of this value if the underlying system
does not distinguish owner and other users.public boolean setExecutable(boolean executable)
setExecutable(boolean, boolean)
public boolean setReadable(boolean readable, boolean ownerOnly)
readable
- To allow read permission if true, otherwise disallowownerOnly
- To manipulate read permission only for owner if true,
otherwise for everyone. The manipulation will apply to
everyone regardless of this value if the underlying system
does not distinguish owner and other users.public boolean setReadable(boolean readable)
setReadable(boolean, boolean)
public boolean setWritable(boolean writable, boolean ownerOnly)
writable
- To allow write permission if true, otherwise disallowownerOnly
- To manipulate write permission only for owner if true,
otherwise for everyone. The manipulation will apply to
everyone regardless of this value if the underlying system
does not distinguish owner and other users.public boolean setWritable(boolean writable)
setWritable(boolean, boolean)
public long length()
public String[] list()
null
if this file is not
a directory.
The entries .
and ..
representing the current and parent
directory are not returned as part of the list.
null
.public String[] list(FilenameFilter filter)
null
if this file is not a directory. If filter
is
null
then all filenames match.
The entries .
and ..
representing the current and parent
directories are not returned as part of the list.
filter
- the filter to match names against, may be null
.null
.public File[] listFiles()
null
if this file is not a directory. The
paths of the files in the array are absolute if the path of this file is
absolute, they are relative otherwise.null
.public File[] listFiles(FilenameFilter filter)
null
if this
file is not a directory. If filter
is null
then all
filenames match.
The entries .
and ..
representing the current and parent
directories are not returned as part of the list.
filter
- the filter to match names against, may be null
.null
.public File[] listFiles(FileFilter filter)
null
if this file is not a
directory. If filter
is null
then all files match.
The entries .
and ..
representing the current and parent
directories are not returned as part of the list.
filter
- the filter to match names against, may be null
.null
.public boolean mkdir()
mkdirs()
if you also want to create missing parents.
Note that this method does not throw IOException
on failure.
Callers must check the return value. Note also that this method returns
false if the directory already existed. If you want to know whether the
directory exists on return, either use (f.mkdir() || f.isDirectory())
or simply ignore the return value from this method and simply call isDirectory()
.
true
if the directory was created,
false
on failure or if the directory already existed.public boolean mkdirs()
mkdir()
if you don't want to create missing parents.
Note that this method does not throw IOException
on failure.
Callers must check the return value. Note also that this method returns
false if the directory already existed. If you want to know whether the
directory exists on return, either use (f.mkdirs() || f.isDirectory())
or simply ignore the return value from this method and simply call isDirectory()
.
true
if the directory was created,
false
on failure or if the directory already existed.public boolean createNewFile() throws IOException
This method is not generally useful. For creating temporary files,
use createTempFile(java.lang.String, java.lang.String)
instead. For reading/writing files, use FileInputStream
,
FileOutputStream
, or RandomAccessFile
, all of which can create files.
Note that this method does not throw IOException
if the file
already exists, even if it's not a regular file. Callers should always check the
return value, and may additionally want to call isFile()
.
IOException
- if it's not possible to create the file.public static File createTempFile(String prefix, String suffix) throws IOException
suffix
is null, .tmp
is used. This
method is a convenience method that calls
createTempFile(String, String, File)
with the third argument
being null
.prefix
- the prefix to the temp file name.suffix
- the suffix to the temp file name.IOException
- if an error occurs when writing the file.public static File createTempFile(String prefix, String suffix, File directory) throws IOException
suffix
is null, .tmp
is used.
Note that this method does not call deleteOnExit()
, but see the
documentation for that method before you call it manually.
prefix
- the prefix to the temp file name.suffix
- the suffix to the temp file name.directory
- the location to which the temp file is to be written, or
null
for the default location for temporary files,
which is taken from the "java.io.tmpdir" system property. It
may be necessary to set this property to an existing, writable
directory for this method to work properly.IllegalArgumentException
- if the length of prefix
is less than 3.IOException
- if an error occurs when writing the file.public boolean renameTo(File newPath)
newPath
. This operation is supported for both
files and directories.
Many failures are possible. Some of the more likely failures include:
Note that this method does not throw IOException
on failure.
Callers must check the return value.
newPath
- the new path.public String toString()
public URI toURI()
@Deprecated public URL toURL() throws MalformedURLException
MalformedURLException
- if the path cannot be transformed into a URL.public long getTotalSpace()
public long getUsableSpace()
Note that this is likely to be an optimistic over-estimate and should not
be taken as a guarantee your application can actually write this many bytes.
On Android (and other Unix-based systems), this method returns the number of free bytes
available to non-root users, regardless of whether you're actually running as root,
and regardless of any quota or other restrictions that might apply to the user.
(The getFreeSpace
method returns the number of bytes potentially available to root.)
public long getFreeSpace()
Note that this is likely to be an optimistic over-estimate and should not be taken as a guarantee your application can actually write this many bytes.