Loading, saving and displaying text - An Introduction to Graphical User Interfaces with Java Swing - page 95

10.1.2 The classes FileReader and FileWriter

The classes FileReader and FileWriter supply methods for reading and writing
ASCII files. These are convenience classes as they make it easy to access files.
The programmer does not have to define a stream explicitly. We start by looking
at a constructor and some methods of class FileReader :

FileReader(File aFile)

void close()
int read()
int read( char [] buffer, int start, int length)

FileReader(File aFile) opens the file aFile for reading. All further methods
refer to this file.

close() stops the file reader and closes the file. It is important not to forget this

!

command, otherwise the file might not be accessible by other applications.

read() reads a single character from the file and returns its integer value (ASCII
code).

read(buffer,start,length) reads length and puts the characters into the
char -array buffer starting at position start of the buffer. Returns the number
of characters read or

− 1ifthe file end is reached.

Most constructors and methods of java.io throw exceptions if errors occur,

!

mostly IOException s. Thus they have to be embedded into try-catch blocks
or the exceptions have to be thrown further.
Class FileWriter supplies methods for writing an ASCII file:

FileWriter(File aFile)

void close()
void write( char [] buffer)
void write( char [] buffer, int start, int length)
void write(String str, int start, int length)

FileWriter(File aFile) - this constructor opens the file aFile for writing. If

!

the file is already present the old content is lost! All further methods refer to
this file.

close() stops the file writer and closes the file. It is important not to forget this

!

command, otherwise part of the data might not be written.

write(char[] buffer) writes the content of the buffer to the file by appending
it to the previously written text.

write(buffer,start,length) writes the number of characters equivalent to the
current value of length from buffer starting at position start of the buffer.
The text is appended to the previously written text.