The Java TM Tutorial

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Trail: Essential Java Classes
Lesson: Reading and Writing (but no 'rithmetic)

## How to Use File Streams

> File streams are perhaps the easiest streams to understand. Simply put, the file streams-- `FileReader`, `FileWriter`, `FileInputStream`, and `FileOutputStream`--each read or write from a file on the native file system. You can create a file stream from a filename, a `File` object, or a `FileDescriptor` object.

> The following `Copy` program uses `FileReader` and `FileWriter` to copy the contents of a file named `farrago.txt` into a file called `outagain.txt`:

> >     import java.io.*;

> >     public class Copy {
> >         public static void main(String[] args) throws IOException {
> >     	File inputFile = new File("farrago.txt");
> >     	File outputFile = new File("outagain.txt");

> >             FileReader in = new FileReader(inputFile);
> >             FileWriter out = new FileWriter(outputFile);
> >             int c;

> >             while ((c = in.read()) != -1)
> >                out.write(c);

> >             in.close();
> >             out.close();
> >         }
> >     }

> This program is very simple. It opens a `FileReader` on `farrago.txt` and opens a `FileWriter` on `outagain.txt`. The program reads characters from the reader as long as there's more input in the input file. When the input runs out, the program closes both the reader and the writer.

> Notice the code that the `Copy` program uses to create a `FileReader`:

> >     File inputFile = new File("farrago.txt");
> >     FileReader in = new FileReader(inputFile);

> This code creates a `File` object that represents the named file on the native file system. `File` is a utility class provided by `java.io`. This program uses this object only to construct a `FileReader` on `farrago.txt`. However, it could use `inputFile` to get information about `farrago.txt`, such as its full pathname.

> After you've run the program, you should find an exact copy of `farrago.txt` in a file named `outagain.txt` in the same directory. Here is the content of the file:

> >     So she went into the garden to cut a cabbage-leaf, to
> >     make an apple-pie; and at the same time a great
> >     she-bear, coming up the street, pops its head into the
> >     shop. 'What! no soap?' So he died, and she very
> >     imprudently married the barber; and there were
> >     present the Picninnies, and the Joblillies, and the
> >     Garyalies, and the grand Panjandrum himself, with the
> >     little round button at top, and they all fell to playing
> >     the game of catch as catch can, till the gun powder ran
> >     out at the heels of their boots.

> >     Samuel Foote 1720-1777

> Remember that `FileReader` and `FileWriter` read and write 16-bit characters. However, most native file systems are based on 8-bit bytes. These streams encode the characters as they operate according to the default character-encoding scheme. You can find out the default character-encoding by using `System.getProperty("file.encoding")`. To specify an encoding other than the default, you should construct an `OutputStreamWriter` on a `FileOutputStream` and specify it. For information about encoding characters, see the Internationalization trail.

> For the curious, here is another version of this program, CopyBytes, which uses `FileInputStream` and `FileOutputStream` in place of `FileReader` and `FileWriter`.

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