The JavaTM Tutorial

| Start of Tutorial > Start of Trail > Start of Lesson | Search Feedback Form

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

## Using Random Access Files

> The `RandomAccessFile` class implements both the `DataInput` and `DataOutput` interfaces and therefore can be used for both reading and writing. `RandomAccessFile` is similar to `FileInputStream` and `FileOutputStream` in that you specify a file on the native file system to open when you create it. You can do this with a file name or a File object. When you create a `RandomAccessFile`, you must indicate whether you will be just reading the file or also writing to it. (You have to be able to read a file in order to write it.) The following code creates a `RandomAccessFile` to read the file named `farrago.txt`:

> >     new RandomAccessFile("farrago.txt", "r");

> And this one opens the same file for both reading and writing:

> >     new RandomAccessFile("farrago.txt", "rw");

> After the file has been opened, you can use the common `read` or `write` methods defined in the `DataInput` and `DataOutput` interfaces to perform I/O on the file.

> `RandomAccessFile` supports the notion of a file pointer. The file pointer indicates the current location in the file. When the file is first created, the file pointer is set to 0, indicating the beginning of the file. Calls to the `read` and `write` methods adjust the file pointer by the number of bytes read or written.

> In addition to the normal file I/O methods that implicitly move the file pointer when the operation occurs, `RandomAccessFile` contains three methods for explicitly manipulating the file pointer.
> - `int skipBytes(int)`--Moves the file pointer forward the specified number of bytes
> - `void seek(long)`--Positions the file pointer just before the specified byte
> - `long getFilePointer()`--Returns the current byte location of the file pointer

| Start of Tutorial > Start of Trail > Start of Lesson | Search Feedback Form

Copyright 1995-2004 Sun Microsystems, Inc. All rights reserved.