The File class is useful for reading and writing external text files.

AccessMode Enumerator

The File Class contains an enumerator that works with file.open to set the mode of a file when it is opened. These items are the argument for an “open” command, and are preceeded with the word “File”. The values are shown:

AccessMode values	Description
ReadOnly	Opens the file as read-only
WriteOnly	Opens the file as write-only. If used with Append, the file is not truncated. If used on its own (or with Truncate), the file is truncated.
ReadWrite	Opens the file in read/write mode. Note that the file is not truncated.
Append	Opens the file in append mode. (WriteOnly must be used with it to make a file appendable: WriteOnly | Append) Useful for writing to a log file.
Truncate	Truncates the file
Translate	Enables carriage returns and line-feed translation for text files in Windows

To open a file object called “f” as write only, issue this command:

f.open(File.WriteOnly | File.Translate);

The Translate flag is needed for Windows files.

Static Functions

Unlike methods, static functions do not reference a specific object. To use any of these commands, precede it with “File.” This indicates that these functions are linked to the File class.

Static Functions	Description
exists(filename)	Boolean: true if fileName exists; false if it does not (filename = string)
remove(filename)	If filename exists, will delete. If not, returns an exception (filename = string)
write(filename, content)	Writes content to the filename. This completely replaces original contents if the file already exists. Returns an exception if can’t write to file. filename = string; content = string
read(filename)	Reads and returns the contents of the file, if possible. If not, returns an exception. filename = string
isFile(filename)	Boolean: true if filename is a file; false if it is not
isDir(filename)	Boolean: true if filename is a directory; false if it is not

For example, to check if a file called “logfile.txt” exists, issue the command:

File.exists(“logfile.txt”);

File Class Properties

All properties in the File class are read only.

File Class Properties	Type	Description
name	String	File name including the extension
path	String	Path of the file
fullName	String	The complete name of the file: path, name, and extension
baseName	String	The name of just the file (no path or extension)
extension	String	Extension of the file name
exists	Boolean	True if the file exists; false if it does not
readable	Boolean	True if the file can be read
writable	Boolean	True if the file can be written
executable	Boolean	True if the file can be executed
hidden	Boolean	True if the file is hidden
eof	Boolean	True if reading has reached the end of the file
created	Date	Time of file creation
lastModified	Date	Last time file was modified
lastRead	Date	Last time file was read
size	Number	Size of file; in bytes

File Class Methods

File Class Methods	Description	data return
new File(filename)	Creates a file object referencing file name; filename = string	no
open(accessMode)	Opens the file using the named accessMode	no
close()	Closes the file	no
readByte()	Reads one byte from the file; Returns a number	yes
read()	Returns the complete contents of the file as a string; if can’t read, returns an exception	yes
readLine()	Reads one line from file if possible; returns an exception if can’t. Trailing whitespace is retained	yes
readLines()	Returns contents of the file as an array of strings--one for each line; Linebreaks are stripped from strings	yes
writeByte(byte)	Writes a byte to the file	no
write(data, length)	Writes length number of characters from data to the file	no
writeLine(data)	Writes the line “data” to the file, and adds a linebreak.	no
copyTo(newName)	copies the current file to "newname" and returns true if the copy was successful	yes

An example of using these commands is given:

f = new File(a.path + "/pressure.txt");

f.open(File.WriteOnly | File.Translate);

f.writeLine("Velocity, Pressure");

f.close();

A step-by-step explanation of this follows:

The following creates a file object called f, and assigns the name “pressure.txt”.

f = new File("pressure.txt");

The file is then opened, and two AccessMode enumerators are used to indicate that this file is write-only, and that it is used in Windows (the Translate modifier):

f.open(File.WriteOnly | File.Translate);

The words “Velocity” and “Pressure” are written to the file to be used as column headers:

f.writeLine("Velocity, Pressure");

The file is closed:

f.close();