RandomAccessFile

RandomAccessFile

java.io

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Java 1.0

closeable

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;   }