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FlexDoc/Javadoc 2.0 Demo Java Doc |
User interfaces and operating systems use system-dependent pathname strings to name files and directories. This class presents an abstract, system-independent view of hierarchical pathnames. An abstract pathname has two components:
The conversion of a pathname string to or from an abstract pathname is inherently system-dependent. When an abstract pathname is converted into a pathname string, each name is separated from the next by a single copy of the default separator character. The default name-separator character is defined by the system property file.separator, and is made available in the public static fields separator and separatorChar of this class. When a pathname string is converted into an abstract pathname, the names within it may be separated by the default name-separator character or by any other name-separator character that is supported by the underlying system.
A pathname, whether abstract or in string form, may be either absolute or relative. An absolute pathname is complete in that no other information is required in order to locate the file that it denotes. A relative pathname, in contrast, must be interpreted in terms of information taken from some other pathname. By default the classes in the java.io package always resolve relative pathnames against the current user directory. This directory is named by the system property user.dir, and is typically the directory in which the Java virtual machine was invoked.
The parent of an abstract pathname may be obtained by invoking the getParent() method of this class and consists of the pathname's prefix and each name in the pathname's name sequence except for the last. Each directory's absolute pathname is an ancestor of any File object with an absolute abstract pathname which begins with the directory's absolute pathname. For example, the directory denoted by the abstract pathname "/usr" is an ancestor of the directory denoted by the pathname "/usr/local/bin".
The prefix concept is used to handle root directories on UNIX platforms, and drive specifiers, root directories and UNC pathnames on Microsoft Windows platforms, as follows:
Instances of this class may or may not denote an actual file-system object such as a file or a directory. If it does denote such an object then that object resides in a partition. A partition is an operating system-specific portion of storage for a file system. A single storage device (e.g. a physical disk-drive, flash memory, CD-ROM) may contain multiple partitions. The object, if any, will reside on the partition named by some ancestor of the absolute form of this pathname.
A file system may implement restrictions to certain operations on the actual file-system object, such as reading, writing, and executing. These restrictions are collectively known as access permissions. The file system may have multiple sets of access permissions on a single object. For example, one set may apply to the object's owner, and another may apply to all other users. The access permissions on an object may cause some methods in this class to fail.
Instances of the File class are immutable; that is, once created, the abstract pathname represented by a File object will never change.
The java.nio.file package defines interfaces and classes for the Java virtual machine to access files, file attributes, and file systems. This API may be used to overcome many of the limitations of the java.io.File class. The toPath method may be used to obtain a Path that uses the abstract path represented by a File object to locate a file. The resulting Path may be used with the Files class to provide more efficient and extensive access to additional file operations, file attributes, and I/O exceptions to help diagnose errors when an operation on a file fails.
Field Summary |
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static final String |
The system-dependent path-separator character, represented as a string
for convenience.
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static final char |
The system-dependent path-separator character.
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static final String |
The system-dependent default name-separator character, represented as a
string for convenience.
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static final char |
The system-dependent default name-separator character.
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Constructor Summary |
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Creates a new File instance from a parent abstract
pathname and a child pathname string.
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Creates a new File instance by converting the given
pathname string into an abstract pathname.
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Creates a new File instance from a parent pathname string
and a child pathname string.
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Creates a new File instance by converting the given
file: URI into an abstract pathname.
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Method Summary |
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boolean |
Tests whether the application can execute the file denoted by this
abstract pathname.
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boolean |
canRead()
Tests whether the application can read the file denoted by this
abstract pathname.
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boolean |
canWrite()
Tests whether the application can modify the file denoted by this
abstract pathname.
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int |
Compares two abstract pathnames lexicographically.
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boolean |
Atomically creates a new, empty file named by this abstract pathname if
and only if a file with this name does not yet exist.
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static File |
Creates an empty file in the default temporary-file directory, using
the given prefix and suffix to generate its name.
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static File |
Creates a new empty file in the specified directory, using the
given prefix and suffix strings to generate its name.
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boolean |
delete()
Deletes the file or directory denoted by this abstract pathname.
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void |
Requests that the file or directory denoted by this abstract
pathname be deleted when the virtual machine terminates.
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boolean |
Tests this abstract pathname for equality with the given object.
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boolean |
exists()
Tests whether the file or directory denoted by this abstract pathname
exists.
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Returns the absolute form of this abstract pathname.
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Returns the absolute pathname string of this abstract pathname.
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Returns the canonical form of this abstract pathname.
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Returns the canonical pathname string of this abstract pathname.
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long |
Returns the number of unallocated bytes in the partition named by this abstract path name.
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getName()
Returns the name of the file or directory denoted by this abstract
pathname.
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Returns the pathname string of this abstract pathname's parent, or
null if this pathname does not name a parent directory.
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Returns the abstract pathname of this abstract pathname's parent,
or null if this pathname does not name a parent
directory.
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getPath()
Converts this abstract pathname into a pathname string.
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long |
Returns the size of the partition named by this
abstract pathname.
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long |
Returns the number of bytes available to this virtual machine on the
partition named by this abstract pathname.
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int |
hashCode()
Computes a hash code for this abstract pathname.
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boolean |
Tests whether this abstract pathname is absolute.
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boolean |
Tests whether the file denoted by this abstract pathname is a
directory.
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boolean |
isFile()
Tests whether the file denoted by this abstract pathname is a normal
file.
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boolean |
isHidden()
Tests whether the file named by this abstract pathname is a hidden
file.
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long |
Returns the time that the file denoted by this abstract pathname was
last modified.
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long |
length()
Returns the length of the file denoted by this abstract pathname.
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String[] |
list()
Returns an array of strings naming the files and directories in the
directory denoted by this abstract pathname.
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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.
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File[] |
Returns an array of abstract pathnames denoting the files in the
directory denoted by this abstract pathname.
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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.
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File[] |
listFiles(FilenameFilter 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.
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static File[] |
List the available filesystem roots.
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boolean |
mkdir()
Creates the directory named by this abstract pathname.
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boolean |
mkdirs()
Creates the directory named by this abstract pathname, including any
necessary but nonexistent parent directories.
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boolean |
Renames the file denoted by this abstract pathname.
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boolean |
setExecutable(boolean executable)
A convenience method to set the owner's execute permission for this
abstract pathname.
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boolean |
setExecutable(boolean executable, boolean ownerOnly)
Sets the owner's or everybody's execute permission for this abstract
pathname.
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boolean |
setLastModified(long time)
Sets the last-modified time of the file or directory named by this
abstract pathname.
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boolean |
setReadable(boolean readable)
A convenience method to set the owner's read permission for this abstract
pathname.
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boolean |
setReadable(boolean readable, boolean ownerOnly)
Sets the owner's or everybody's read permission for this abstract
pathname.
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boolean |
Marks the file or directory named by this abstract pathname so that
only read operations are allowed.
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boolean |
setWritable(boolean writable)
A convenience method to set the owner's write permission for this abstract
pathname.
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boolean |
setWritable(boolean writable, boolean ownerOnly)
Sets the owner's or everybody's write permission for this abstract
pathname.
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toPath()
Returns a java.nio.file.Path object constructed from
this abstract path.
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toString()
Returns the pathname string of this abstract pathname.
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toURI()
Constructs a file: URI that represents this abstract pathname.
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toURL()
Deprecated. This method does not automatically escape characters that
are illegal in URLs.
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Methods inherited from class java.lang.Object |
public File |
(String pathname) |
public File |
If parent is null then the new File instance is created as if by invoking the single-argument File constructor on the given child pathname string.
Otherwise the parent pathname string is taken to denote a directory, and the child pathname string is taken to denote either a directory or a file. If the child pathname string is absolute then it is converted into a relative pathname in a system-dependent way. If parent is the empty string then the new File instance is created by converting child into an abstract pathname and resolving the result against a system-dependent default directory. Otherwise each pathname string is converted into an abstract pathname and the child abstract pathname is resolved against the parent.
public File |
If parent is null then the new File instance is created as if by invoking the single-argument File constructor on the given child pathname string.
Otherwise the parent abstract pathname is taken to denote a directory, and the child pathname string is taken to denote either a directory or a file. If the child pathname string is absolute then it is converted into a relative pathname in a system-dependent way. If parent is the empty abstract pathname then the new File instance is created by converting child into an abstract pathname and resolving the result against a system-dependent default directory. Otherwise each pathname string is converted into an abstract pathname and the child abstract pathname is resolved against the parent.
public File |
(URI uri) |
The exact form of a file: URI is system-dependent, hence the transformation performed by this constructor is also system-dependent.
For a given abstract pathname f it is guaranteed that
so long as the original abstract pathname, the URI, and the new abstract pathname are all created in (possibly different invocations of) the same Java virtual machine. This relationship typically does not hold, however, when a file: URI that is created in a virtual machine on one operating system is converted into an abstract pathname in a virtual machine on a different operating system.new File(
f.toURI()).equals(
f.getAbsoluteFile())
public String getName |
() |
public String getParent |
() |
The parent of an abstract pathname consists of the pathname's prefix, if any, and each name in the pathname's name sequence except for the last. If the name sequence is empty then the pathname does not name a parent directory.
public File getParentFile |
() |
The parent of an abstract pathname consists of the pathname's prefix, if any, and each name in the pathname's name sequence except for the last. If the name sequence is empty then the pathname does not name a parent directory.
public String getPath |
() |
public boolean isAbsolute |
() |
public String getAbsolutePath |
() |
If this abstract pathname is already absolute, then the pathname string is simply returned as if by the getPath() method. If this abstract pathname is the empty abstract pathname then the pathname string of the current user directory, which is named by the system property user.dir, is returned. Otherwise this pathname is resolved in a system-dependent way. On UNIX systems, a relative pathname is made absolute by resolving it against the current user directory. On Microsoft Windows systems, a relative pathname is made absolute by resolving it against the current directory of the drive named by the pathname, if any; if not, it is resolved against the current user directory.
public File getAbsoluteFile |
() |
new File(this.getAbsolutePath())
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public String getCanonicalPath |
() |
throws |
A canonical pathname is both absolute and unique. The precise definition of canonical form is system-dependent. This method first converts this pathname to absolute form if necessary, as if by invoking the getAbsolutePath() method, and then maps it to its unique form in a system-dependent way. This typically involves removing redundant names such as "." and ".." from the pathname, resolving symbolic links (on UNIX platforms), and converting drive letters to a standard case (on Microsoft Windows platforms).
Every pathname that denotes an existing file or directory has a unique canonical form. Every pathname that denotes a nonexistent file or directory also has a unique canonical form. The canonical form of the pathname of a nonexistent file or directory may be different from the canonical form of the same pathname after the file or directory is created. Similarly, the canonical form of the pathname of an existing file or directory may be different from the canonical form of the same pathname after the file or directory is deleted.
public File getCanonicalFile |
() |
throws |
new File(this.getCanonicalPath())
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public URL toURL |
() |
throws |
public URI toURI |
() |
The exact form of the URI is system-dependent. If it can be determined that the file denoted by this abstract pathname is a directory, then the resulting URI will end with a slash.
For a given abstract pathname f, it is guaranteed that
so long as the original abstract pathname, the URI, and the new abstract pathname are all created in (possibly different invocations of) the same Java virtual machine. Due to the system-dependent nature of abstract pathnames, however, this relationship typically does not hold when a file: URI that is created in a virtual machine on one operating system is converted into an abstract pathname in a virtual machine on a different operating system.new File(
f.toURI()).equals(
f.getAbsoluteFile())
Note that when this abstract pathname represents a UNC pathname then all components of the UNC (including the server name component) are encoded in the URI path. The authority component is undefined, meaning that it is represented as null. The Path class defines the toUri method to encode the server name in the authority component of the resulting URI. The toPath method may be used to obtain a Path representing this abstract pathname.
public boolean canRead |
() |
public boolean canWrite |
() |
public boolean exists |
() |
public boolean isDirectory |
() |
Where it is required to distinguish an I/O exception from the case that the file is not a directory, or where several attributes of the same file are required at the same time, then the Files.readAttributes method may be used.
public boolean isFile |
() |
Where it is required to distinguish an I/O exception from the case that the file is not a normal file, or where several attributes of the same file are required at the same time, then the Files.readAttributes method may be used.
public boolean isHidden |
() |
public long lastModified |
() |
public long length |
() |
Where it is required to distinguish an I/O exception from the case that 0L is returned, or where several attributes of the same file are required at the same time, then the Files.readAttributes method may be used.
public boolean createNewFile |
() |
throws |
Note: this method should not be used for file-locking, as the resulting protocol cannot be made to work reliably. The FileLock facility should be used instead.
public boolean delete |
() |
Note that the Files class defines the delete method to throw an IOException when a file cannot be deleted. This is useful for error reporting and to diagnose why a file cannot be deleted.
public void deleteOnExit |
() |
Once deletion has been requested, it is not possible to cancel the request. This method should therefore be used with care.
Note: this method should not be used for file-locking, as the resulting protocol cannot be made to work reliably. The FileLock facility should be used instead.
public String[] list |
() |
If this abstract pathname does not denote a directory, then this method returns null. Otherwise an array of strings is returned, one for each file or directory in the directory. Names denoting the directory itself and the directory's parent directory are not included in the result. Each string is a file name rather than a complete path.
There is no guarantee that the name strings in the resulting array will appear in any specific order; they are not, in particular, guaranteed to appear in alphabetical order.
Note that the Files class defines the newDirectoryStream method to open a directory and iterate over the names of the files in the directory. This may use less resources when working with very large directories, and may be more responsive when working with remote directories.
public String[] list |
(FilenameFilter filter) |
public File[] listFiles |
() |
If this abstract pathname does not denote a directory, then this method returns null. Otherwise an array of File objects is returned, one for each file or directory in the directory. Pathnames denoting the directory itself and the directory's parent directory are not included in the result. Each resulting abstract pathname is constructed from this abstract pathname using the File(File, String) constructor. Therefore if this pathname is absolute then each resulting pathname is absolute; if this pathname is relative then each resulting pathname will be relative to the same directory.
There is no guarantee that the name strings in the resulting array will appear in any specific order; they are not, in particular, guaranteed to appear in alphabetical order.
Note that the Files class defines the newDirectoryStream method to open a directory and iterate over the names of the files in the directory. This may use less resources when working with very large directories.
public File[] listFiles |
(FilenameFilter filter) |
public File[] listFiles |
(FileFilter filter) |
public boolean mkdir |
() |
public boolean mkdirs |
() |
public boolean renameTo |
(File dest) |
Many aspects of the behavior of this method are inherently platform-dependent: The rename operation might not be able to move a file from one filesystem to another, it might not be atomic, and it might not succeed if a file with the destination abstract pathname already exists. The return value should always be checked to make sure that the rename operation was successful. As instances of File are immutable, this File object is not changed to name the destination file or directory.
Note that the Files class defines the move method to move or rename a file in a platform independent manner.
public boolean setLastModified |
(long time) |
All platforms support file-modification times to the nearest second, but some provide more precision. The argument will be truncated to fit the supported precision. If the operation succeeds and no intervening operations on the file take place, then the next invocation of the lastModified() method will return the (possibly truncated) time argument that was passed to this method.
public boolean setReadOnly |
() |
public boolean setWritable |
(boolean writable, boolean ownerOnly) |
The Files class defines methods that operate on file attributes including file permissions. This may be used when finer manipulation of file permissions is required.
public boolean setWritable |
(boolean writable) |
An invocation of this method of the form file.setWritable(arg) behaves in exactly the same way as the invocation
file.setWritable(arg, true)
public boolean setReadable |
(boolean readable, boolean ownerOnly) |
The Files class defines methods that operate on file attributes including file permissions. This may be used when finer manipulation of file permissions is required.
public boolean setReadable |
(boolean readable) |
An invocation of this method of the form file.setReadable(arg) behaves in exactly the same way as the invocation
file.setReadable(arg, true)
public boolean setExecutable |
(boolean executable, boolean ownerOnly) |
The Files class defines methods that operate on file attributes including file permissions. This may be used when finer manipulation of file permissions is required.
public boolean setExecutable |
(boolean executable) |
An invocation of this method of the form file.setExcutable(arg) behaves in exactly the same way as the invocation
file.setExecutable(arg, true)
public boolean canExecute |
() |
public static File[] listRoots |
() |
A particular Java platform may support zero or more hierarchically-organized file systems. Each file system has a root directory from which all other files in that file system can be reached. Windows platforms, for example, have a root directory for each active drive; UNIX platforms have a single root directory, namely "/". The set of available filesystem roots is affected by various system-level operations such as the insertion or ejection of removable media and the disconnecting or unmounting of physical or virtual disk drives.
This method returns an array of File objects that denote the root directories of the available filesystem roots. It is guaranteed that the canonical pathname of any file physically present on the local machine will begin with one of the roots returned by this method.
The canonical pathname of a file that resides on some other machine and is accessed via a remote-filesystem protocol such as SMB or NFS may or may not begin with one of the roots returned by this method. If the pathname of a remote file is syntactically indistinguishable from the pathname of a local file then it will begin with one of the roots returned by this method. Thus, for example, File objects denoting the root directories of the mapped network drives of a Windows platform will be returned by this method, while File objects containing UNC pathnames will not be returned by this method.
Unlike most methods in this class, this method does not throw security exceptions. If a security manager exists and its SecurityManager.checkRead(String) method denies read access to a particular root directory, then that directory will not appear in the result.
public long getTotalSpace |
() |
public long getFreeSpace |
() |
The returned number of unallocated bytes is a hint, but not a guarantee, that it is possible to use most or any of these bytes. The number of unallocated bytes is most likely to be accurate immediately after this call. It is likely to be made inaccurate by any external I/O operations including those made on the system outside of this virtual machine. This method makes no guarantee that write operations to this file system will succeed.
public long getUsableSpace |
() |
The returned number of available bytes is a hint, but not a guarantee, that it is possible to use most or any of these bytes. The number of available bytes is most likely to be accurate immediately after this call. It is likely to be made inaccurate by any external I/O operations including those made on the system outside of this virtual machine. This method makes no guarantee that write operations to this file system will succeed.
public static File createTempFile |
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throws |
Creates a new empty file in the specified directory, using the given prefix and suffix strings to generate its name. If this method returns successfully then it is guaranteed that:
The prefix argument must be at least three characters long. It is recommended that the prefix be a short, meaningful string such as "hjb" or "mail". The suffix argument may be null, in which case the suffix ".tmp" will be used.
To create the new file, the prefix and the suffix may first be adjusted to fit the limitations of the underlying platform. If the prefix is too long then it will be truncated, but its first three characters will always be preserved. If the suffix is too long then it too will be truncated, but if it begins with a period character ('.') then the period and the first three characters following it will always be preserved. Once these adjustments have been made the name of the new file will be generated by concatenating the prefix, five or more internally-generated characters, and the suffix.
If the directory argument is null then the system-dependent default temporary-file directory will be used. The default temporary-file directory is specified by the system property java.io.tmpdir. On UNIX systems the default value of this property is typically "/tmp" or "/var/tmp"; on Microsoft Windows systems it is typically "C:\\WINNT\\TEMP". A different value may be given to this system property when the Java virtual machine is invoked, but programmatic changes to this property are not guaranteed to have any effect upon the temporary directory used by this method.
public static File createTempFile |
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throws |
The Files.createTempFile method provides an alternative method to create an empty file in the temporary-file directory. Files created by that method may have more restrictive access permissions to files created by this method and so may be more suited to security-sensitive applications.
public int compareTo |
(File pathname) |
public boolean equals |
(Object obj) |
public int hashCode |
() |
public String toString |
() |
public Path toPath |
() |
The first invocation of this method works as if invoking it were equivalent to evaluating the expression:
Subsequent invocations of this method return the same Path.FileSystems.getDefault().getPath(this.getPath());
If this abstract pathname is the empty abstract pathname then this method returns a Path that may be used to access the current user directory.
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FlexDoc/Javadoc 2.0 Demo Java Doc |