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Chapter 11 The java.io Package |
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Chapter 11 The java.io Package |
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java.io.File
java.lang.Object
None
None
JDK 1.0 or later
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().
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();
}
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 ";".
This variable holds the first (and only) character in pathSeparator.
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 "\".
This variable holds the first (and only) character in separator.
A full pathname (i.e., a directory and filename).
This constructor creates a File object that represents the file specified by path.
A directory path.
A filename.
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.
A File object that represents a directory.
A filename.
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.
A boolean value that indicates if the file is readable.
If the application does not have permission to read the File.
This method returns true if File corresponds to an existing, readable file or directory. Otherwise it returns false.
A boolean value that indicates if the file is writable.
If the application does not have permission to write to the File.
This method returns true if File corresponds to an existing, writable file or directory. Otherwise it returns false.
true if the file is deleted; otherwise false.
If the application does not have permission to delete the file.
This method attempts to delete the file or directory associated with this File object. A directory is only deleted if it is empty.
The Object to be compared.
true if the objects are equal; false if they are not.
Object.equals()
This method returns true if obj is an instance of File that encapsulates the same pathname as this object.
true if the file or directory exists; false otherwise.
If the application does not have permission to read the File.
This method returns true if this File corresponds to an existing file or directory.
A String that contains the absolute pathname.
This method returns the absolute pathname of the file or directory associated with this File.
New as of JDK 1.1
A String that contains the canonical, or exact, pathname.
If any kind of I/O error occurs.
This method returns the canonical pathname of the file or directory associated with this File.
A String that contains the filename.
This method returns the filename associated with this File. The string returned does not include the name of the directory.
A String that contains the parent directory of the file, or null if it does not exist.
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.
A String that contains the pathname of the file.
This method returns the full pathname associated with this File.
A hashcode value for this file.
Object.hashCode()
This method returns a hashcode based on the pathname associated with this File.
true if the File represents an absolute path; false otherwise.
This method indicates if the File represents an absolute path; what constitutes an absolute path is system-dependent.
true if the File represents a directory; false otherwise.
If the application does not have permission to read the File.
This method returns true if this File corresponds to a directory.
true if the File represents a normal file; false otherwise.
If the application does not have permission to read the File.
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.
The time the file was last modified, or 0L if the file does not exist.
If the application does not have permission to read the File.
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.
The file length, in bytes, or 0L if the file does not exist.
If the application does not have permission to read the File.
This method returns the length of the file or directory that corresponds to this File.
An array of the names of the files and directories contained by this File, or null if this File is not a directory.
If the application does not have permission to read the File.
This method returns the contents of a directory. The current directory and the parent directory are not included in the list.
A filter to use.
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.
If the application does not have permission to read the File.
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().
true if the directory is created; false otherwise.
If the application does not have permission to write to the File.
This method creates a directory with the pathname specified by this File.
true if the directory is created; false otherwise.
If the application does not have permission to write to the File.
This method creates a directory with the pathname specified by this File. The method also creates all the parent directories if necessary.
A File that specifies the new name.
true if the name is changed; false otherwise.
If the application does not have permission to write to this File or the file represented by dest.
This method changes the pathname of this File to the pathname specified by dest.
A String that contains the pathname of this File.
Object.toString()
This method returns a string representation of this File object.
|
Method |
Inherited From |
Method |
Inherited From |
|---|---|---|---|
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clone() |
Object |
finalize() |
Object |
|
getClass() |
Object |
notify() |
Object |
|
notifyAll() |
Object |
wait() |
Object |
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wait(long) |
Object |
wait(long, int) |
Object |
FileInputStream, FilenameFilter, FileOutputStream, FileReader, FileWriter, IOException, SecurityException
|
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|
| Externalizable |  |
FileDescriptor |
