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 filename 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 line of Java 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 readXXX or writeXXX methods 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 0, indicating the beginning of the file. Calls to the readXXX and writeXXX 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.

skipBytes
Moves the file pointer forward the specified number of bytes.
seek
Positions the file pointer just before the specified byte.
getFilePointer
Returns the current byte location of the file pointer.

Input and Output Streams