This class allows you to read and write arbitrary bytes, text, and primitive Java data types from or to any specified location in a file. Because this class provides random, rather than sequential, access to files, it is neither a subclass of InputStream nor of OutputStream, but provides an entirely independent method for reading and writing data from or to files. RandomAccessFile implements the same interfaces as DataInputStream and DataOutputStream, and thus defines the same methods for reading and writing data as those classes do.

The seek( ) method provides random access to the file; it is used to select the position in the file where data should be read or written. The various read and write methods update this file position so that a sequence of read or write operations can be performed on a contiguous portion of the file without having to call the seek( ) method before each read or write.

The mode argument to the constructor methods should be "r" for a file that is to be read-only or "rw" for a file that is to be written (and perhaps read as well). In Java 1.4 and later, two other values for the mode argument are allowed as well. A mode of "rwd" opens the file for reading and writing, and requires that (if the file resides on a local filesystem) every update to the file content be written synchronously to the underlying file. The "rws" mode is similar, but requires synchronous updates to both the file's content and its metadata (which includes things such as file access times). Using "rws" mode may require that the file metadata be modified every time the file is read.

In Java 1.4 and later, use the getChannel( ) method to obtain a FileChannel object that you can use to access the file using the New I/O API of java.nio and its subpackages. If the RandomAccessFile was opened with a mode of "r", the FileChannel allows only reading. Otherwise, it allows both reading and writing.

Figure 9-53. java.io.RandomAccessFile

public class RandomAccessFile implements Closeable, DataInput, DataOutput {
// Public Constructors
     public RandomAccessFile(File file, String mode) throws FileNotFoundException;  
     public RandomAccessFile(String name, String mode) throws FileNotFoundException;  
// Public Instance Methods
     public void close( ) throws IOException;          Implements:Closeable
1.4  public final java.nio.channels.FileChannel getChannel( );  
     public final FileDescriptor getFD( ) throws IOException;  
     public long getFilePointer( ) throws IOException;                    native
     public long length( ) throws IOException;                            native
     public int read( ) throws IOException;                               native
     public int read(byte[ ] b) throws IOException;  
     public int read(byte[ ] b, int off, int len) throws IOException;  
     public void seek(long pos) throws IOException;                     native
1.2  public void setLength(long newLength) throws IOException;      native
// Methods Implementing Closeable
     public void close( ) throws IOException;  
// Methods Implementing DataInput
     public final boolean readBoolean( ) throws IOException;  
     public final byte readByte( ) throws IOException;  
     public final char readChar( ) throws IOException;  
     public final double readDouble( ) throws IOException;  
     public final float readFloat( ) throws IOException;  
     public final void readFully(byte[ ] b) throws IOException;  
     public final void readFully(byte[ ] b, int off, int len) throws IOException;  
     public final int readInt( ) throws IOException;  
     public final String readLine( ) throws IOException;  
     public final long readLong( ) throws IOException;  
     public final short readShort( ) throws IOException;  
     public final int readUnsignedByte( ) throws IOException;  
     public final int readUnsignedShort( ) throws IOException;  
     public final String readUTF( ) throws IOException;  
     public int skipBytes(int n) throws IOException;  
// Methods Implementing DataOutput
     public void write(int b) throws IOException;                       native
     public void write(byte[ ] b) throws IOException;  
     public void write(byte[ ] b, int off, int len) throws IOException;  
     public final void writeBoolean(boolean v) throws IOException;  
     public final void writeByte(int v) throws IOException;  
     public final void writeBytes(String s) throws IOException;  
     public final void writeChar(int v) throws IOException;  
     public final void writeChars(String s) throws IOException;  
     public final void writeDouble(double v) throws IOException;  
     public final void writeFloat(float v) throws IOException;  
     public final void writeInt(int v) throws IOException;  
     public final void writeLong(long v) throws IOException;  
     public final void writeShort(int v) throws IOException;  
     public final void writeUTF(String str) throws IOException;  
}