libjava/java/io/RandomAccessFile.java

   1 /* RandomAccessFile.java -- Class supporting random file I/O
   2    Copyright (C) 1998, 1999, 2001, 2002, 2003 Free Software Foundation, Inc.
   3
   4 This file is part of GNU Classpath.
   5
   6 GNU Classpath is free software; you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation; either version 2, or (at your option)
   9 any later version.
  10
  11 GNU Classpath is distributed in the hope that it will be useful, but
  12 WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14 General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GNU Classpath; see the file COPYING.  If not, write to the
  18 Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  19 02111-1307 USA.
  20
  21 Linking this library statically or dynamically with other modules is
  22 making a combined work based on this library.  Thus, the terms and
  23 conditions of the GNU General Public License cover the whole
  24 combination.
  25
  26 As a special exception, the copyright holders of this library give you
  27 permission to link this library with independent modules to produce an
  28 executable, regardless of the license terms of these independent
  29 modules, and to copy and distribute the resulting executable under
  30 terms of your choice, provided that you also meet, for each linked
  31 independent module, the terms and conditions of the license of that
  32 module.  An independent module is a module which is not derived from
  33 or based on this library.  If you modify this library, you may extend
  34 this exception to your version of the library, but you are not
  35 obligated to do so.  If you do not wish to do so, delete this
  36 exception statement from your version. */
  37
  38
  39 package java.io;
  40
  41 import java.nio.channels.FileChannel;
  42 import java.nio.channels.FileChannelImpl;
  43
  44 /* Written using "Java Class Libraries", 2nd edition, ISBN 0-201-31002-3
  45  * "The Java Language Specification", ISBN 0-201-63451-1
  46  * Status: Believe complete and correct to 1.1.
  47  */
  48
  49 /**
  50  * This class allows reading and writing of files at random locations.
  51  * Most Java I/O classes are either pure sequential input or output.  This
  52  * class fulfills the need to be able to read the bytes of a file in an
  53  * arbitrary order.  In addition, this class implements the
  54  * <code>DataInput</code> and <code>DataOutput</code> interfaces to allow
  55  * the reading and writing of Java primitives.
  56  *
  57  * @author Aaron M. Renn <arenn@urbanophile.com>
  58  * @author Tom Tromey <tromey@cygnus.com>
  59  */
  60 public class RandomAccessFile implements DataOutput, DataInput
  61 {
  62
  63   // The underlying file.
  64   private FileDescriptor fd;
  65   // The corresponding input and output streams.
  66   private DataOutputStream out;
  67   private DataInputStream in;
  68
  69   private FileChannel ch; /* cached associated file-channel */
  70
  71   /**
  72    * This method initializes a new instance of <code>RandomAccessFile</code>
  73    * to read from the specified <code>File</code> object with the specified
  74    * access mode.   The access mode is either "r" for read only access or "rw"
  75    * for read-write access.
  76    * <p>
  77    * Note that a <code>SecurityManager</code> check is made prior to
  78    * opening the file to determine whether or not this file is allowed to
  79    * be read or written.
  80    *
  81    * @param file The <code>File</code> object to read and/or write.
  82    * @param mode "r" for read only or "rw" for read-write access to the file
  83    *
  84    * @exception IllegalArgumentException If <code>mode</code> has an
  85    * illegal value
  86    * @exception SecurityException If the requested access to the file
  87    * is not allowed
  88    * @exception IOException If any other error occurs
  89    */
  90   public RandomAccessFile (File file, String mode)
  91     throws FileNotFoundException
  92   {
  93     this (file.getPath(), mode);
  94   }
  95
  96   /**
  97    * This method initializes a new instance of <code>RandomAccessFile</code>
  98    * to read from the specified file name with the specified access mode.
  99    * The access mode is either "r" for read only access, "rw" for read
 100    * write access, "rws" for synchronized read/write access of both
 101    * content and metadata, or "rwd" for read/write access
 102    * where only content is required to be synchronous.
 103    * <p>
 104    * Note that a <code>SecurityManager</code> check is made prior to
 105    * opening the file to determine whether or not this file is allowed to
 106    * be read or written.
 107    *
 108    * @param fileName The name of the file to read and/or write
 109    * @param mode "r", "rw", "rws", or "rwd"
 110    *
 111    * @exception IllegalArgumentException If <code>mode</code> has an
 112    * illegal value
 113    * @exception SecurityException If the requested access to the file
 114    * is not allowed
 115    * @exception FileNotFoundException If any other error occurs
 116    */
 117   public RandomAccessFile (String fileName, String mode)
 118     throws FileNotFoundException
 119   {
 120     int fdmode;
 121     if (mode.equals("r"))
 122       fdmode = FileDescriptor.READ;
 123     else if (mode.equals("rw"))
 124       fdmode = FileDescriptor.READ | FileDescriptor.WRITE;
 125     else if (mode.equals("rws"))
 126       {
 127         fdmode = (FileDescriptor.READ | FileDescriptor.WRITE
 128                   | FileDescriptor.SYNC);
 129       }
 130     else if (mode.equals("rwd"))
 131       {
 132         fdmode = (FileDescriptor.READ | FileDescriptor.WRITE
 133                   | FileDescriptor.DSYNC);
 134       }
 135     else
 136       throw new IllegalArgumentException ("invalid mode: " + mode);
 137
 138     // The obligatory SecurityManager stuff
 139     SecurityManager s = System.getSecurityManager();
 140     if (s != null)
 141       {
 142         s.checkRead(fileName);
 143
 144         if ((fdmode & FileDescriptor.WRITE) != 0)
 145           s.checkWrite(fileName);
 146       }
 147
 148     fd = new FileDescriptor (fileName, fdmode);
 149     out = new DataOutputStream (new FileOutputStream (fd));
 150     in = new DataInputStream (new FileInputStream (fd));
 151   }
 152
 153   /**
 154    * This method closes the file and frees up all file related system
 155    * resources.  Since most operating systems put a limit on how many files
 156    * may be opened at any given time, it is a good idea to close all files
 157    * when no longer needed to avoid hitting this limit
 158    */
 159   public void close () throws IOException
 160   {
 161     if (fd.valid())
 162       fd.close();
 163   }
 164
 165   /**
 166    * This method returns a <code>FileDescriptor</code> object that
 167    * represents the native file handle for this file.
 168    *
 169    * @return The <code>FileDescriptor</code> object for this file
 170    *
 171    * @exception IOException If an error occurs
 172    */
 173   public final FileDescriptor getFD () throws IOException
 174   {
 175     if (! fd.valid())
 176       throw new IOException ();
 177
 178     return fd;
 179   }
 180
 181   /**
 182    * This method returns the current offset in the file at which the next
 183    * read or write will occur
 184    *
 185    * @return The current file position
 186    *
 187    * @exception IOException If an error occurs
 188    */
 189   public long getFilePointer () throws IOException
 190   {
 191     return fd.getFilePointer();
 192   }
 193
 194   /**
 195    * This method sets the length of the file to the specified length.  If
 196    * the currently length of the file is longer than the specified length,
 197    * then the file is truncated to the specified length.  If the current
 198    * length of the file is shorter than the specified length, the file
 199    * is extended with bytes of an undefined value.
 200    *  <p>
 201    * The file must be open for write access for this operation to succeed.
 202    *
 203    * @param newlen The new length of the file
 204    *
 205    * @exception IOException If an error occurs
 206    */
 207   public void setLength (long newLen) throws IOException
 208   {
 209     fd.setLength (newLen);
 210   }
 211
 212   /**
 213    * This method returns the length of the file in bytes
 214    *
 215    * @return The length of the file
 216    *
 217    * @exception IOException If an error occurs
 218    */
 219   public long length () throws IOException
 220   {
 221     return fd.getLength ();
 222   }
 223
 224   /**
 225    * This method reads a single byte of data from the file and returns it
 226    * as an integer.
 227    *
 228    * @return The byte read as an int, or -1 if the end of the file was reached.
 229    *
 230    * @exception IOException If an error occurs
 231    */
 232   public int read () throws IOException
 233   {
 234     return in.read();
 235   }
 236
 237   /**
 238    * This method reads bytes from the file into the specified array.  The
 239    * bytes are stored starting at the beginning of the array and up to
 240    * <code>buf.length</code> bytes can be read.
 241    *
 242    * @param buf The buffer to read bytes from the file into
 243    *
 244    * @return The actual number of bytes read or -1 if end of file
 245    *
 246    * @exception IOException If an error occurs
 247    */
 248   public int read (byte[] buffer) throws IOException
 249   {
 250     return in.read (buffer);
 251   }
 252
 253   /**
 254    * This methods reads up to <code>len</code> bytes from the file into the
 255    * specified array starting at position <code>offset</code> into the array.
 256    *
 257    * @param buf The array to read the bytes into
 258    * @param offset The index into the array to start storing bytes
 259    * @param len The requested number of bytes to read
 260    *
 261    * @return The actual number of bytes read, or -1 if end of file
 262    *
 263    * @exception IOException If an error occurs
 264    */
 265   public int read (byte[] buffer, int offset, int len) throws IOException
 266   {
 267     return in.read (buffer, offset, len);
 268   }
 269
 270   /**
 271    * This method reads a Java boolean value from an input stream.  It does
 272    * so by reading a single byte of data.  If that byte is zero, then the
 273    * value returned is <code>false</code>  If the byte is non-zero, then
 274    * the value returned is <code>true</code>
 275    * <p>
 276    * This method can read a <code>boolean</code> written by an object
 277    * implementing the
 278    * <code>writeBoolean()</code> method in the <code>DataOutput</code>
 279    * interface.
 280    *
 281    * @return The <code>boolean</code> value read
 282    *
 283    * @exception EOFException If end of file is reached before reading the
 284    * boolean
 285    * @exception IOException If any other error occurs
 286    */
 287   public final boolean readBoolean () throws IOException
 288   {
 289     return in.readBoolean ();
 290   }
 291
 292   /**
 293    * This method reads a Java byte value from an input stream.  The value
 294    * is in the range of -128 to 127.
 295    * <p>
 296    * This method can read a <code>byte</code> written by an object
 297    * implementing the
 298    * <code>writeByte()</code> method in the <code>DataOutput</code> interface.
 299    *
 300    * @return The <code>byte</code> value read
 301    *
 302    * @exception EOFException If end of file is reached before reading the byte
 303    * @exception IOException If any other error occurs
 304    *
 305    * @see DataOutput
 306    */
 307   public final byte readByte () throws IOException
 308   {
 309     return in.readByte ();
 310   }
 311
 312   /**
 313    * This method reads a Java <code>char</code> value from an input stream.
 314    * It operates by reading two bytes from the stream and converting them to
 315    * a single 16-bit Java <code>char</code>  The two bytes are stored most
 316    * significant byte first (i.e., "big endian") regardless of the native
 317    * host byte ordering.
 318    * <p>
 319    * As an example, if <code>byte1</code> and code{byte2</code> represent
 320    * the first
 321    * and second byte read from the stream respectively, they will be
 322    * transformed to a <code>char</code> in the following manner:
 323    * <p>
 324    * <code>(char)(((byte1 & 0xFF) << 8) | (byte2 & 0xFF)</code>
 325    * <p>
 326    * This method can read a <code>char</code> written by an object
 327    * implementing the
 328    * <code>writeChar()</code> method in the <code>DataOutput</code> interface.
 329    *
 330    * @return The <code>char</code> value read
 331    *
 332    * @exception EOFException If end of file is reached before reading the char
 333    * @exception IOException If any other error occurs
 334    *
 335    * @see DataOutput
 336    */
 337   public final char readChar () throws IOException
 338   {
 339     return in.readChar();
 340   }
 341
 342   /**
 343    * This method reads a Java double value from an input stream.  It operates
 344    * by first reading a <code>logn</code> value from the stream by calling the
 345    * <code>readLong()</code> method in this interface, then
 346    * converts that <code>long</code>
 347    * to a <code>double</code> using the <code>longBitsToDouble</code>
 348    * method in the class <code>java.lang.Double</code>
 349    * <p>
 350    * This method can read a <code>double</code> written by an object
 351    * implementing the
 352    * <code>writeDouble()</code> method in the <code>DataOutput</code>
 353    * interface.
 354    *
 355    * @return The <code>double</code> value read
 356    *
 357    * @exception EOFException If end of file is reached before reading
 358    * the double
 359    * @exception IOException If any other error occurs
 360    *
 361    * @see java.lang.Double
 362    * @see DataOutput
 363    */
 364   public final double readDouble () throws IOException
 365   {
 366     return in.readDouble ();
 367   }
 368
 369   /**
 370    * This method reads a Java float value from an input stream.  It operates
 371    * by first reading an <code>int</code> value from the stream by calling the
 372    * <code>readInt()</code> method in this interface, then converts
 373    * that <code>int</code>
 374    * to a <code>float</code> using the <code>intBitsToFloat</code> method in
 375    * the class <code>java.lang.Float</code>
 376    * <p>
 377    * This method can read a <code>float</code> written by an object
 378    * implementing the
 379    * <code>writeFloat()</code> method in the <code>DataOutput</code> interface.
 380    *
 381    * @return The <code>float</code> value read
 382    *
 383    * @exception EOFException If end of file is reached before reading the float
 384    * @exception IOException If any other error occurs
 385    *
 386    * @see java.lang.Float
 387    * @see DataOutput
 388    */
 389   public final float readFloat () throws IOException
 390   {
 391     return in.readFloat();
 392   }
 393
 394   /**
 395    * This method reads raw bytes into the passed array until the array is
 396    * full.  Note that this method blocks until the data is available and
 397    * throws an exception if there is not enough data left in the stream to
 398    * fill the buffer
 399    *
 400    * @param buf The buffer into which to read the data
 401    *
 402    * @exception EOFException If end of file is reached before filling the
 403    * buffer
 404    * @exception IOException If any other error occurs
 405    */
 406   public final void readFully (byte[] buffer) throws IOException
 407   {
 408     in.readFully(buffer);
 409   }
 410
 411   /**
 412    * This method reads raw bytes into the passed array <code>buf</code>
 413    * starting
 414    * <code>offset</code> bytes into the buffer.  The number of bytes read
 415    * will be
 416    * exactly <code>len</code>  Note that this method blocks until the data is
 417    * available and throws an exception if there is not enough data left in
 418    * the stream to read <code>len</code> bytes.
 419    *
 420    * @param buf The buffer into which to read the data
 421    * @param offset The offset into the buffer to start storing data
 422    * @param len The number of bytes to read into the buffer
 423    *
 424    * @exception EOFException If end of file is reached before filling
 425    * the buffer
 426    * @exception IOException If any other error occurs
 427    */
 428   public final void readFully (byte[] buffer, int offset, int count)
 429     throws IOException
 430   {
 431     in.readFully (buffer, offset, count);
 432   }
 433
 434   /**
 435    * This method reads a Java <code>int</code> value from an input stream
 436    * It operates by reading four bytes from the stream and converting them to
 437    * a single Java <code>int</code>  The bytes are stored most
 438    * significant byte first (i.e., "big endian") regardless of the native
 439    * host byte ordering.
 440    * <p>
 441    * As an example, if <code>byte1</code> through <code>byte4</code>
 442    * represent the first
 443    * four bytes read from the stream, they will be
 444    * transformed to an <code>int</code> in the following manner:
 445    * <p>
 446    * <code>(int)(((byte1 & 0xFF) << 24) + ((byte2 & 0xFF) << 16) +
 447    * ((byte3 & 0xFF) << 8) + (byte4 & 0xFF)))</code>
 448    * <p>
 449    * The value returned is in the range of 0 to 65535.
 450    * <p>
 451    * This method can read an <code>int</code> written by an object
 452    * implementing the
 453    * <code>writeInt()</code> method in the <code>DataOutput</code> interface.
 454    *
 455    * @return The <code>int</code> value read
 456    *
 457    * @exception EOFException If end of file is reached before reading the int
 458    * @exception IOException If any other error occurs
 459    *
 460    * @see DataOutput
 461    */
 462   public final int readInt () throws IOException
 463   {
 464     return in.readInt();
 465   }
 466
 467   /**
 468    * This method reads the next line of text data from an input stream.
 469    * It operates by reading bytes and converting those bytes to
 470    * <code>char</code>
 471    * values by treating the byte read as the low eight bits of the
 472    * <code>char</code>
 473    * and using <code>0</code> as the high eight bits.  Because of this, it does
 474    * not support the full 16-bit Unicode character set.
 475    * <p>
 476    * The reading of bytes ends when either the end of file or a line terminator
 477    * is encountered.  The bytes read are then returned as a <code>String</code>
 478    * A line terminator is a byte sequence consisting of either
 479    * <code>\r</code> <code>\n</code> or <code>\r\n</code>  These
 480    * termination charaters are
 481    * discarded and are not returned as part of the string.
 482    * <p>
 483    * This method can read data that was written by an object implementing the
 484    * <code>writeLine()</code> method in <code>DataOutput</code>
 485    *
 486    * @return The line read as a <code>String</code>
 487    *
 488    * @exception IOException If an error occurs
 489    *
 490    * @see DataOutput
 491    */
 492   public final String readLine () throws IOException
 493   {
 494     return in.readLine ();
 495   }
 496
 497   /**
 498    * This method reads a Java long value from an input stream
 499    * It operates by reading eight bytes from the stream and converting them to
 500    * a single Java <code>long</code>  The bytes are stored most
 501    * significant byte first (i.e., "big endian") regardless of the native
 502    * host byte ordering.
 503    * <p>
 504    * As an example, if <code>byte1</code> through <code>byte8</code>
 505    * represent the first
 506    * eight bytes read from the stream, they will be
 507    * transformed to an <code>long</code> in the following manner:
 508    * <p>
 509    * <code>
 510    * (long)((((long)byte1 & 0xFF) << 56) + (((long)byte2 & 0xFF) << 48) +
 511    * (((long)byte3 & 0xFF) << 40) + (((long)byte4 & 0xFF) << 32) +
 512    * (((long)byte5 & 0xFF) << 24) + (((long)byte6 & 0xFF) << 16) +
 513    * (((long)byte7 & 0xFF) << 8) + ((long)byte9 & 0xFF)))</code>
 514    * <p>
 515    * The value returned is in the range of 0 to 65535.
 516    * <p>
 517    * This method can read an <code>long</code> written by an object
 518    * implementing the
 519    * <code>writeLong()</code> method in the <code>DataOutput</code> interface.
 520    *
 521    * @return The <code>long</code> value read
 522    *
 523    * @exception EOFException If end of file is reached before reading the long
 524    * @exception IOException If any other error occurs
 525    *
 526    * @see DataOutput
 527    */
 528   public final long readLong () throws IOException
 529   {
 530     return in.readLong();
 531   }
 532
 533   /**
 534    * This method reads a signed 16-bit value into a Java in from the stream.
 535    * It operates by reading two bytes from the stream and converting them to
 536    * a single 16-bit Java <code>short</code>  The two bytes are stored most
 537    * significant byte first (i.e., "big endian") regardless of the native
 538    * host byte ordering.
 539    * <p>
 540    * As an example, if <code>byte1</code> and code{byte2</code>
 541    * represent the first
 542    * and second byte read from the stream respectively, they will be
 543    * transformed to a <code>short</code> in the following manner:
 544    * <p>
 545    * <code>(short)(((byte1 & 0xFF) << 8) | (byte2 & 0xFF)</code>
 546    * <p>
 547    * The value returned is in the range of -32768 to 32767.
 548    * <p>
 549    * This method can read a <code>short</code> written by an object
 550    * implementing the
 551    * <code>writeShort()</code> method in the <code>DataOutput</code> interface.
 552    *
 553    * @return The <code>short</code> value read
 554    *
 555    * @exception EOFException If end of file is reached before reading the value
 556    * @exception IOException If any other error occurs
 557    *
 558    * @see DataOutput
 559    */
 560   public final short readShort () throws IOException
 561   {
 562     return in.readShort();
 563   }
 564
 565   /**
 566    * This method reads 8 unsigned bits into a Java <code>int</code> value
 567    * from the
 568    * stream. The value returned is in the range of 0 to 255.
 569    * <p>
 570    * This method can read an unsigned byte written by an object implementing
 571    * the <code>writeUnsignedByte()</code> method in the
 572    * <code>DataOutput</code> interface.
 573    *
 574    * @return The unsigned bytes value read as a Java <code>int</code>
 575    *
 576    * @exception EOFException If end of file is reached before reading the value
 577    * @exception IOException If any other error occurs
 578    *
 579    * @see DataOutput
 580    */
 581   public final int readUnsignedByte () throws IOException
 582   {
 583     return in.readUnsignedByte();
 584   }
 585
 586   /**
 587    * This method reads 16 unsigned bits into a Java int value from the stream.
 588    * It operates by reading two bytes from the stream and converting them to
 589    * a single Java <code>int</code>  The two bytes are stored most
 590    * significant byte first (i.e., "big endian") regardless of the native
 591    * host byte ordering.
 592    * <p>
 593    * As an example, if <code>byte1</code> and <code>byte2</code>
 594    * represent the first
 595    * and second byte read from the stream respectively, they will be
 596    * transformed to an <code>int</code> in the following manner:
 597    * <p>
 598    * <code>(int)(((byte1 & 0xFF) << 8) + (byte2 & 0xFF))</code>
 599    * <p>
 600    * The value returned is in the range of 0 to 65535.
 601    * <p>
 602    * This method can read an unsigned short written by an object implementing
 603    * the <code>writeUnsignedShort()</code> method in the
 604    * <code>DataOutput</code> interface.
 605    *
 606    * @return The unsigned short value read as a Java <code>int</code>
 607    *
 608    * @exception EOFException If end of file is reached before reading the value
 609    * @exception IOException If any other error occurs
 610    */
 611   public final int readUnsignedShort () throws IOException
 612   {
 613     return in.readUnsignedShort();
 614   }
 615
 616   /**
 617    * This method reads a <code>String</code> from an input stream that
 618    * is encoded in
 619    * a modified UTF-8 format.  This format has a leading two byte sequence
 620    * that contains the remaining number of bytes to read.  This two byte
 621    * sequence is read using the <code>readUnsignedShort()</code> method of this
 622    * interface.
 623    * <p>
 624    * After the number of remaining bytes have been determined, these bytes
 625    * are read an transformed into <code>char</code> values.
 626    * These <code>char</code> values
 627    * are encoded in the stream using either a one, two, or three byte format.
 628    * The particular format in use can be determined by examining the first
 629    * byte read.
 630    * <p>
 631    * If the first byte has a high order bit of 0 then
 632    * that character consists on only one byte.  This character value consists
 633    * of seven bits that are at positions 0 through 6 of the byte.  As an
 634    * example, if <code>byte1</code> is the byte read from the stream, it would
 635    * be converted to a <code>char</code> like so:
 636    * <p>
 637    * <code>(char)byte1</code>
 638    * <p>
 639    * If the first byte has <code>110</code> as its high order bits, then the
 640    * character consists of two bytes.  The bits that make up the character
 641    * value are in positions 0 through 4 of the first byte and bit positions
 642    * 0 through 5 of the second byte.  (The second byte should have
 643    * 10 as its high order bits).  These values are in most significant
 644    * byte first (i.e., "big endian") order.
 645    * <p>
 646    * As an example, if <code>byte1</code> and <code>byte2</code>
 647    * are the first two bytes
 648    * read respectively, and the high order bits of them match the patterns
 649    * which indicate a two byte character encoding, then they would be
 650    * converted to a Java <code>char</code> like so:
 651    * <p>
 652    * <code>(char)(((byte1 & 0x1F) << 6) | (byte2 & 0x3F))</code>
 653    * <p>
 654    * If the first byte has a <code>1110</code> as its high order bits, then the
 655    * character consists of three bytes.  The bits that make up the character
 656    * value are in positions 0 through 3 of the first byte and bit positions
 657    * 0 through 5 of the other two bytes.  (The second and third bytes should
 658    * have <code>10</code> as their high order bits).  These values are in most
 659    * significant byte first (i.e., "big endian") order.
 660    * <p>
 661    * As an example, if <code>byte1</code> <code>byte2</code>
 662    * and <code>byte3</code> are the
 663    * three bytes read, and the high order bits of them match the patterns
 664    * which indicate a three byte character encoding, then they would be
 665    * converted to a Java <code>char</code> like so:
 666    * <p>
 667    * <code>(char)(((byte1 & 0x0F) << 12) | ((byte2 & 0x3F) << 6) |
 668    * (byte3 & 0x3F))</code>
 669    * <p>
 670    * Note that all characters are encoded in the method that requires the
 671    * fewest number of bytes with the exception of the character with the
 672    * value of <code>&#92;u0000</code> which is encoded as two bytes.  This is
 673    * a  modification of the UTF standard used to prevent C language style
 674    * <code>NUL</code> values from appearing in the byte stream.
 675    * <p>
 676    * This method can read data that was written by an object implementing the
 677    * <code>writeUTF()</code> method in <code>DataOutput</code>
 678    *
 679    * @return The <code>String</code> read
 680    *
 681    * @exception EOFException If end of file is reached before reading the
 682    * String
 683    * @exception UTFDataFormatException If the data is not in UTF-8 format
 684    * @exception IOException If any other error occurs
 685    *
 686    * @see DataOutput
 687    */
 688   public final String readUTF () throws IOException
 689   {
 690     return in.readUTF();
 691   }
 692
 693   /**
 694    * This method sets the current file position to the specified offset
 695    * from the beginning of the file.  Note that some operating systems will
 696    * allow the file pointer to be set past the current end of the file.
 697    *
 698    * @param pos The offset from the beginning of the file at which to set
 699    * the file pointer
 700    *
 701    * @exception IOException If an error occurs
 702    */
 703   public void seek (long pos) throws IOException
 704   {
 705     fd.seek (pos, FileDescriptor.SET, false);
 706   }
 707
 708   /**
 709    * This method attempts to skip and discard the specified number of bytes
 710    * in the input stream.  It may actually skip fewer bytes than requested.
 711    * The actual number of bytes skipped is returned.  This method will not
 712    * skip any bytes if passed a negative number of bytes to skip.
 713    *
 714    * @param numBytes The requested number of bytes to skip.
 715    *
 716    * @return The number of bytes actually skipped.
 717    *
 718    * @exception IOException If an error occurs.
 719    */
 720   public int skipBytes (int numBytes) throws IOException
 721   {
 722     if (numBytes < 0)
 723       throw new IllegalArgumentException ("Can't skip negative bytes: " +
 724                                           numBytes);
 725
 726     if (numBytes == 0)
 727       return 0;
 728
 729     long curPos = fd.getFilePointer ();
 730     long newPos = fd.seek (numBytes, FileDescriptor.CUR, true);
 731
 732     return (int) (newPos - curPos);
 733   }
 734
 735   /**
 736    * This method writes a single byte of data to the file. The file must
 737    * be open for read-write in order for this operation to succeed.
 738    *
 739    * @param The byte of data to write, passed as an int.
 740    *
 741    * @exception IOException If an error occurs
 742    */
 743   public void write (int oneByte) throws IOException
 744   {
 745     out.write(oneByte);
 746   }
 747
 748   /**
 749    * This method writes all the bytes in the specified array to the file.
 750    * The file must be open read-write in order for this operation to succeed.
 751    *
 752    * @param buf The array of bytes to write to the file
 753    */
 754   public void write (byte[] buffer) throws IOException
 755   {
 756     out.write(buffer);
 757   }
 758
 759   /**
 760    * This method writes <code>len</code> bytes to the file from the specified
 761    * array starting at index <code>offset</code> into the array.
 762    *
 763    * @param buf The array of bytes to write to the file
 764    * @param offset The index into the array to start writing file
 765    * @param len The number of bytes to write
 766    *
 767    * @exception IOException If an error occurs
 768    */
 769   public void write (byte[] buffer, int offset, int len) throws IOException
 770   {
 771     out.write (buffer, offset, len);
 772   }
 773
 774   /**
 775    * This method writes a Java <code>boolean</code> to the underlying output
 776    * stream. For a value of <code>true</code>, 1 is written to the stream.
 777    * For a value of <code>false</code>, 0 is written.
 778    *
 779    * @param b The <code>boolean</code> value to write to the stream
 780    *
 781    * @exception IOException If an error occurs
 782    */
 783   public final void writeBoolean (boolean val) throws IOException
 784   {
 785     out.writeBoolean(val);
 786   }
 787
 788   /**
 789    * This method writes a Java <code>byte</code> value to the underlying
 790    * output stream.
 791    *
 792    * @param b The <code>byte</code> to write to the stream, passed
 793    * as an <code>int</code>.
 794    *
 795    * @exception IOException If an error occurs
 796    */
 797   public final void writeByte (int v) throws IOException
 798   {
 799     out.writeByte(v);
 800   }
 801
 802   /**
 803    * This method writes a Java <code>short</code> to the stream, high byte
 804    * first.  This method requires two bytes to encode the value.
 805    *
 806    * @param s The <code>short</code> value to write to the stream,
 807    * passed as an <code>int</code>.
 808    *
 809    * @exception IOException If an error occurs
 810    */
 811   public final void writeShort (int v) throws IOException
 812   {
 813     out.writeShort(v);
 814   }
 815
 816   /**
 817    * This method writes a single <code>char</code> value to the stream,
 818    * high byte first.
 819    *
 820    * @param v The <code>char</code> value to write, passed as
 821    * an <code>int</code>.
 822    *
 823    * @exception IOException If an error occurs
 824    */
 825   public final void writeChar (int v) throws IOException
 826   {
 827     out.writeChar(v);
 828   }
 829
 830   /**
 831    * This method writes a Java <code>int</code> to the stream, high bytes
 832    * first.  This method requires four bytes to encode the value.
 833    *
 834    * @param v The <code>int</code> value to write to the stream.
 835    *
 836    * @exception IOException If an error occurs
 837    */
 838   public final void writeInt (int v) throws IOException
 839   {
 840     out.writeInt(v);
 841   }
 842
 843   /**
 844    * This method writes a Java <code>long</code> to the stream, high bytes
 845    * first.  This method requires eight bytes to encode the value.
 846    *
 847    * @param v The <code>long</code> value to write to the stream.
 848    *
 849    * @exception IOException If an error occurs
 850    */
 851   public final void writeLong (long v) throws IOException
 852   {
 853     out.writeLong(v);
 854   }
 855
 856   /**
 857    * This method writes a Java <code>float</code> value to the stream.  This
 858    * value is written by first calling the method
 859    * <code>Float.floatToIntBits</code>
 860    * to retrieve an <code>int</code> representing the floating point number,
 861    * then writing this <code>int</code> value to the stream exactly the same
 862    * as the <code>writeInt()</code> method does.
 863    *
 864    * @param v The floating point number to write to the stream.
 865    *
 866    * @exception IOException If an error occurs
 867    *
 868    * @see #writeInt(int)
 869    */
 870   public final void writeFloat (float v) throws IOException
 871   {
 872     out.writeFloat(v);
 873   }
 874
 875   /**
 876    * This method writes a Java <code>double</code> value to the stream.  This
 877    * value is written by first calling the method
 878    * <code>Double.doubleToLongBits</code>
 879    * to retrieve an <code>long</code> representing the floating point number,
 880    * then writing this <code>long</code> value to the stream exactly the same
 881    * as the <code>writeLong()</code> method does.
 882    *
 883    * @param v The double precision floating point number to write to the
 884    * stream.
 885    *
 886    * @exception IOException If an error occurs
 887    *
 888    * @see #writeLong(long)
 889    */
 890   public final void writeDouble (double v) throws IOException
 891   {
 892     out.writeDouble(v);
 893   }
 894
 895   /**
 896    * This method writes all the bytes in a <code>String</code> out to the
 897    * stream.  One byte is written for each character in the <code>String</code>.
 898    * The high eight bits of each character are discarded.
 899    *
 900    * @param s The <code>String</code> to write to the stream
 901    *
 902    * @exception IOException If an error occurs
 903    */
 904   public final void writeBytes (String s) throws IOException
 905   {
 906     out.writeBytes(s);
 907   }
 908
 909   /**
 910    * This method writes all the characters in a <code>String</code> to the
 911    * stream.  There will be two bytes for each character value.  The high
 912    * byte of the character will be written first.
 913    *
 914    * @param s The <code>String</code> to write to the stream.
 915    *
 916    * @exception IOException If an error occurs
 917    */
 918   public final void writeChars (String s) throws IOException
 919   {
 920     out.writeChars(s);
 921   }
 922
 923   /**
 924    * This method writes a Java <code>String</code> to the stream in a modified
 925    * UTF-8 format.  First, two bytes are written to the stream indicating the
 926    * number of bytes to follow.  Note that this is the number of bytes in the
 927    * encoded <code>String</code> not the <code>String</code> length.  Next
 928    * come the encoded characters.  Each character in the <code>String</code>
 929    * is encoded as either one, two or three bytes.  For characters in the
 930    * range of <code>&#92;u0001</code> to <code>&#92;u007F</code>,
 931    * one byte is used.  The character
 932    * value goes into bits 0-7 and bit eight is 0.  For characters in the range
 933    * of <code>&#92;u0080</code> to <code>&#92;u007FF</code>, two
 934    * bytes are used.  Bits
 935    * 6-10 of the character value are encoded bits 0-4 of the first byte, with
 936    * the high bytes having a value of "110".  Bits 0-5 of the character value
 937    * are stored in bits 0-5 of the second byte, with the high bits set to
 938    * "10".  This type of encoding is also done for the null character
 939    * <code>&#92;u0000</code>.  This eliminates any C style NUL character values
 940    * in the output.  All remaining characters are stored as three bytes.
 941    * Bits 12-15 of the character value are stored in bits 0-3 of the first
 942    * byte.  The high bits of the first bytes are set to "1110".  Bits 6-11
 943    * of the character value are stored in bits 0-5 of the second byte.  The
 944    * high bits of the second byte are set to "10".  And bits 0-5 of the
 945    * character value are stored in bits 0-5 of byte three, with the high bits
 946    * of that byte set to "10".
 947    *
 948    * @param s The <code>String</code> to write to the output in UTF format
 949    *
 950    * @exception IOException If an error occurs
 951    */
 952   public final void writeUTF (String s) throws IOException
 953   {
 954     out.writeUTF(s);
 955   }
 956
 957   /**
 958    * This method creates a java.nio.channels.FileChannel.
 959    * Nio does not allow one to create a file channel directly.
 960    * A file channel must be created by first creating an instance of
 961    * Input/Output/RandomAccessFile and invoking the getChannel() method on it.
 962    */
 963   public final synchronized FileChannel getChannel ()
 964   {
 965     if (ch == null)
 966       ch = new FileChannelImpl (fd, true, this);
 967
 968     return ch;
 969   }
 970
 971 } // class RandomAccessFile
 972