1 /*
   2  * Copyright (c) 1994, 2013, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 
  26 package java.io;
  27 
  28 import java.nio.channels.FileChannel;
  29 import sun.nio.ch.FileChannelImpl;
  30 
  31 
  32 /**
  33  * Instances of this class support both reading and writing to a
  34  * random access file. A random access file behaves like a large
  35  * array of bytes stored in the file system. There is a kind of cursor,
  36  * or index into the implied array, called the <em>file pointer</em>;
  37  * input operations read bytes starting at the file pointer and advance
  38  * the file pointer past the bytes read. If the random access file is
  39  * created in read/write mode, then output operations are also available;
  40  * output operations write bytes starting at the file pointer and advance
  41  * the file pointer past the bytes written. Output operations that write
  42  * past the current end of the implied array cause the array to be
  43  * extended. The file pointer can be read by the
  44  * {@code getFilePointer} method and set by the {@code seek}
  45  * method.
  46  * <p>
  47  * It is generally true of all the reading routines in this class that
  48  * if end-of-file is reached before the desired number of bytes has been
  49  * read, an {@code EOFException} (which is a kind of
  50  * {@code IOException}) is thrown. If any byte cannot be read for
  51  * any reason other than end-of-file, an {@code IOException} other
  52  * than {@code EOFException} is thrown. In particular, an
  53  * {@code IOException} may be thrown if the stream has been closed.
  54  *
  55  * @author  unascribed
  56  * @since   JDK1.0
  57  */
  58 
  59 public class RandomAccessFile implements DataOutput, DataInput, Closeable {
  60 
  61     private FileDescriptor fd;
  62     private FileChannel channel = null;
  63     private boolean rw;
  64 
  65     private Object closeLock = new Object();
  66     private volatile boolean closed = false;
  67 
  68     private static final int O_RDONLY = 1;
  69     private static final int O_RDWR =   2;
  70     private static final int O_SYNC =   4;
  71     private static final int O_DSYNC =  8;
  72 
  73     /**
  74      * Creates a random access file stream to read from, and optionally
  75      * to write to, a file with the specified name. A new
  76      * {@link FileDescriptor} object is created to represent the
  77      * connection to the file.
  78      *
  79      * <p> The <tt>mode</tt> argument specifies the access mode with which the
  80      * file is to be opened.  The permitted values and their meanings are as
  81      * specified for the <a
  82      * href="#mode"><tt>RandomAccessFile(File,String)</tt></a> constructor.
  83      *
  84      * <p>
  85      * If there is a security manager, its {@code checkRead} method
  86      * is called with the {@code name} argument
  87      * as its argument to see if read access to the file is allowed.
  88      * If the mode allows writing, the security manager's
  89      * {@code checkWrite} method
  90      * is also called with the {@code name} argument
  91      * as its argument to see if write access to the file is allowed.
  92      *
  93      * @param      name   the system-dependent filename
  94      * @param      mode   the access <a href="#mode">mode</a>
  95      * @exception  IllegalArgumentException  if the mode argument is not equal
  96      *               to one of <tt>"r"</tt>, <tt>"rw"</tt>, <tt>"rws"</tt>, or
  97      *               <tt>"rwd"</tt>
  98      * @exception FileNotFoundException
  99      *            if the mode is <tt>"r"</tt> but the given string does not
 100      *            denote an existing regular file, or if the mode begins with
 101      *            <tt>"rw"</tt> but the given string does not denote an
 102      *            existing, writable regular file and a new regular file of
 103      *            that name cannot be created, or if some other error occurs
 104      *            while opening or creating the file
 105      * @exception  SecurityException         if a security manager exists and its
 106      *               {@code checkRead} method denies read access to the file
 107      *               or the mode is "rw" and the security manager's
 108      *               {@code checkWrite} method denies write access to the file
 109      * @see        java.lang.SecurityException
 110      * @see        java.lang.SecurityManager#checkRead(java.lang.String)
 111      * @see        java.lang.SecurityManager#checkWrite(java.lang.String)
 112      * @revised 1.4
 113      * @spec JSR-51
 114      */
 115     public RandomAccessFile(String name, String mode)
 116         throws FileNotFoundException
 117     {
 118         this(name != null ? new File(name) : null, mode);
 119     }
 120 
 121     /**
 122      * Creates a random access file stream to read from, and optionally to
 123      * write to, the file specified by the {@link File} argument.  A new {@link
 124      * FileDescriptor} object is created to represent this file connection.
 125      *
 126      * <p>The <a name="mode"><tt>mode</tt></a> argument specifies the access mode
 127      * in which the file is to be opened.  The permitted values and their
 128      * meanings are:
 129      *
 130      * <table summary="Access mode permitted values and meanings">
 131      * <tr><th align="left">Value</th><th align="left">Meaning</th></tr>
 132      * <tr><td valign="top"><tt>"r"</tt></td>
 133      *     <td> Open for reading only.  Invoking any of the <tt>write</tt>
 134      *     methods of the resulting object will cause an {@link
 135      *     java.io.IOException} to be thrown. </td></tr>
 136      * <tr><td valign="top"><tt>"rw"</tt></td>
 137      *     <td> Open for reading and writing.  If the file does not already
 138      *     exist then an attempt will be made to create it. </td></tr>
 139      * <tr><td valign="top"><tt>"rws"</tt></td>
 140      *     <td> Open for reading and writing, as with <tt>"rw"</tt>, and also
 141      *     require that every update to the file's content or metadata be
 142      *     written synchronously to the underlying storage device.  </td></tr>
 143      * <tr><td valign="top"><tt>"rwd"&nbsp;&nbsp;</tt></td>
 144      *     <td> Open for reading and writing, as with <tt>"rw"</tt>, and also
 145      *     require that every update to the file's content be written
 146      *     synchronously to the underlying storage device. </td></tr>
 147      * </table>
 148      *
 149      * The <tt>"rws"</tt> and <tt>"rwd"</tt> modes work much like the {@link
 150      * java.nio.channels.FileChannel#force(boolean) force(boolean)} method of
 151      * the {@link java.nio.channels.FileChannel} class, passing arguments of
 152      * <tt>true</tt> and <tt>false</tt>, respectively, except that they always
 153      * apply to every I/O operation and are therefore often more efficient.  If
 154      * the file resides on a local storage device then when an invocation of a
 155      * method of this class returns it is guaranteed that all changes made to
 156      * the file by that invocation will have been written to that device.  This
 157      * is useful for ensuring that critical information is not lost in the
 158      * event of a system crash.  If the file does not reside on a local device
 159      * then no such guarantee is made.
 160      *
 161      * <p>The <tt>"rwd"</tt> mode can be used to reduce the number of I/O
 162      * operations performed.  Using <tt>"rwd"</tt> only requires updates to the
 163      * file's content to be written to storage; using <tt>"rws"</tt> requires
 164      * updates to both the file's content and its metadata to be written, which
 165      * generally requires at least one more low-level I/O operation.
 166      *
 167      * <p>If there is a security manager, its {@code checkRead} method is
 168      * called with the pathname of the {@code file} argument as its
 169      * argument to see if read access to the file is allowed.  If the mode
 170      * allows writing, the security manager's {@code checkWrite} method is
 171      * also called with the path argument to see if write access to the file is
 172      * allowed.
 173      *
 174      * @param      file   the file object
 175      * @param      mode   the access mode, as described
 176      *                    <a href="#mode">above</a>
 177      * @exception  IllegalArgumentException  if the mode argument is not equal
 178      *               to one of <tt>"r"</tt>, <tt>"rw"</tt>, <tt>"rws"</tt>, or
 179      *               <tt>"rwd"</tt>
 180      * @exception FileNotFoundException
 181      *            if the mode is <tt>"r"</tt> but the given file object does
 182      *            not denote an existing regular file, or if the mode begins
 183      *            with <tt>"rw"</tt> but the given file object does not denote
 184      *            an existing, writable regular file and a new regular file of
 185      *            that name cannot be created, or if some other error occurs
 186      *            while opening or creating the file
 187      * @exception  SecurityException         if a security manager exists and its
 188      *               {@code checkRead} method denies read access to the file
 189      *               or the mode is "rw" and the security manager's
 190      *               {@code checkWrite} method denies write access to the file
 191      * @see        java.lang.SecurityManager#checkRead(java.lang.String)
 192      * @see        java.lang.SecurityManager#checkWrite(java.lang.String)
 193      * @see        java.nio.channels.FileChannel#force(boolean)
 194      * @revised 1.4
 195      * @spec JSR-51
 196      */
 197     public RandomAccessFile(File file, String mode)
 198         throws FileNotFoundException
 199     {
 200         String name = (file != null ? file.getPath() : null);
 201         int imode = -1;
 202         if (mode.equals("r"))
 203             imode = O_RDONLY;
 204         else if (mode.startsWith("rw")) {
 205             imode = O_RDWR;
 206             rw = true;
 207             if (mode.length() > 2) {
 208                 if (mode.equals("rws"))
 209                     imode |= O_SYNC;
 210                 else if (mode.equals("rwd"))
 211                     imode |= O_DSYNC;
 212                 else
 213                     imode = -1;
 214             }
 215         }
 216         if (imode < 0)
 217             throw new IllegalArgumentException("Illegal mode \"" + mode
 218                                                + "\" must be one of "
 219                                                + "\"r\", \"rw\", \"rws\","
 220                                                + " or \"rwd\"");
 221         SecurityManager security = System.getSecurityManager();
 222         if (security != null) {
 223             security.checkRead(name);
 224             if (rw) {
 225                 security.checkWrite(name);
 226             }
 227         }
 228         if (name == null) {
 229             throw new NullPointerException();
 230         }
 231         if (file.isInvalid()) {
 232             throw new FileNotFoundException("Invalid file path");
 233         }
 234         fd = new FileDescriptor();
 235         fd.attach(this);
 236         open(name, imode);
 237     }
 238 
 239     /**
 240      * Returns the opaque file descriptor object associated with this
 241      * stream.
 242      *
 243      * @return     the file descriptor object associated with this stream.
 244      * @exception  IOException  if an I/O error occurs.
 245      * @see        java.io.FileDescriptor
 246      */
 247     public final FileDescriptor getFD() throws IOException {
 248         if (fd != null) {
 249             return fd;
 250         }
 251         throw new IOException();
 252     }
 253 
 254     /**
 255      * Returns the unique {@link java.nio.channels.FileChannel FileChannel}
 256      * object associated with this file.
 257      *
 258      * <p> The {@link java.nio.channels.FileChannel#position()
 259      * position} of the returned channel will always be equal to
 260      * this object's file-pointer offset as returned by the {@link
 261      * #getFilePointer getFilePointer} method.  Changing this object's
 262      * file-pointer offset, whether explicitly or by reading or writing bytes,
 263      * will change the position of the channel, and vice versa.  Changing the
 264      * file's length via this object will change the length seen via the file
 265      * channel, and vice versa.
 266      *
 267      * @return  the file channel associated with this file
 268      *
 269      * @since 1.4
 270      * @spec JSR-51
 271      */
 272     public final FileChannel getChannel() {
 273         synchronized (this) {
 274             if (channel == null) {
 275                 channel = FileChannelImpl.open(fd, true, rw, this);
 276             }
 277             return channel;
 278         }
 279     }
 280 
 281     /**
 282      * Opens a file and returns the file descriptor.  The file is
 283      * opened in read-write mode if the O_RDWR bit in {@code mode}
 284      * is true, else the file is opened as read-only.
 285      * If the {@code name} refers to a directory, an IOException
 286      * is thrown.
 287      *
 288      * @param name the name of the file
 289      * @param mode the mode flags, a combination of the O_ constants
 290      *             defined above
 291      */
 292     private native void open(String name, int mode)
 293         throws FileNotFoundException;
 294 
 295     // 'Read' primitives
 296 
 297     /**
 298      * Reads a byte of data from this file. The byte is returned as an
 299      * integer in the range 0 to 255 ({@code 0x00-0x0ff}). This
 300      * method blocks if no input is yet available.
 301      * <p>
 302      * Although {@code RandomAccessFile} is not a subclass of
 303      * {@code InputStream}, this method behaves in exactly the same
 304      * way as the {@link InputStream#read()} method of
 305      * {@code InputStream}.
 306      *
 307      * @return     the next byte of data, or {@code -1} if the end of the
 308      *             file has been reached.
 309      * @exception  IOException  if an I/O error occurs. Not thrown if
 310      *                          end-of-file has been reached.
 311      */
 312     public native int read() throws IOException;
 313 
 314     /**
 315      * Reads a sub array as a sequence of bytes.
 316      * @param b the buffer into which the data is read.
 317      * @param off the start offset of the data.
 318      * @param len the number of bytes to read.
 319      * @exception IOException If an I/O error has occurred.
 320      */
 321     private native int readBytes(byte b[], int off, int len) throws IOException;
 322 
 323     /**
 324      * Reads up to {@code len} bytes of data from this file into an
 325      * array of bytes. This method blocks until at least one byte of input
 326      * is available.
 327      * <p>
 328      * Although {@code RandomAccessFile} is not a subclass of
 329      * {@code InputStream}, this method behaves in exactly the
 330      * same way as the {@link InputStream#read(byte[], int, int)} method of
 331      * {@code InputStream}.
 332      *
 333      * @param      b     the buffer into which the data is read.
 334      * @param      off   the start offset in array {@code b}
 335      *                   at which the data is written.
 336      * @param      len   the maximum number of bytes read.
 337      * @return     the total number of bytes read into the buffer, or
 338      *             {@code -1} if there is no more data because the end of
 339      *             the file has been reached.
 340      * @exception  IOException If the first byte cannot be read for any reason
 341      * other than end of file, or if the random access file has been closed, or if
 342      * some other I/O error occurs.
 343      * @exception  NullPointerException If {@code b} is {@code null}.
 344      * @exception  IndexOutOfBoundsException If {@code off} is negative,
 345      * {@code len} is negative, or {@code len} is greater than
 346      * {@code b.length - off}
 347      */
 348     public int read(byte b[], int off, int len) throws IOException {
 349         return readBytes(b, off, len);
 350     }
 351 
 352     /**
 353      * Reads up to {@code b.length} bytes of data from this file
 354      * into an array of bytes. This method blocks until at least one byte
 355      * of input is available.
 356      * <p>
 357      * Although {@code RandomAccessFile} is not a subclass of
 358      * {@code InputStream}, this method behaves in exactly the
 359      * same way as the {@link InputStream#read(byte[])} method of
 360      * {@code InputStream}.
 361      *
 362      * @param      b   the buffer into which the data is read.
 363      * @return     the total number of bytes read into the buffer, or
 364      *             {@code -1} if there is no more data because the end of
 365      *             this file has been reached.
 366      * @exception  IOException If the first byte cannot be read for any reason
 367      * other than end of file, or if the random access file has been closed, or if
 368      * some other I/O error occurs.
 369      * @exception  NullPointerException If {@code b} is {@code null}.
 370      */
 371     public int read(byte b[]) throws IOException {
 372         return readBytes(b, 0, b.length);
 373     }
 374 
 375     /**
 376      * Reads {@code b.length} bytes from this file into the byte
 377      * array, starting at the current file pointer. This method reads
 378      * repeatedly from the file until the requested number of bytes are
 379      * read. This method blocks until the requested number of bytes are
 380      * read, the end of the stream is detected, or an exception is thrown.
 381      *
 382      * @param      b   the buffer into which the data is read.
 383      * @exception  EOFException  if this file reaches the end before reading
 384      *               all the bytes.
 385      * @exception  IOException   if an I/O error occurs.
 386      */
 387     public final void readFully(byte b[]) throws IOException {
 388         readFully(b, 0, b.length);
 389     }
 390 
 391     /**
 392      * Reads exactly {@code len} bytes from this file into the byte
 393      * array, starting at the current file pointer. This method reads
 394      * repeatedly from the file until the requested number of bytes are
 395      * read. This method blocks until the requested number of bytes are
 396      * read, the end of the stream is detected, or an exception is thrown.
 397      *
 398      * @param      b     the buffer into which the data is read.
 399      * @param      off   the start offset of the data.
 400      * @param      len   the number of bytes to read.
 401      * @exception  EOFException  if this file reaches the end before reading
 402      *               all the bytes.
 403      * @exception  IOException   if an I/O error occurs.
 404      */
 405     public final void readFully(byte b[], int off, int len) throws IOException {
 406         int n = 0;
 407         do {
 408             int count = this.read(b, off + n, len - n);
 409             if (count < 0)
 410                 throw new EOFException();
 411             n += count;
 412         } while (n < len);
 413     }
 414 
 415     /**
 416      * Attempts to skip over {@code n} bytes of input discarding the
 417      * skipped bytes.
 418      * <p>
 419      *
 420      * This method may skip over some smaller number of bytes, possibly zero.
 421      * This may result from any of a number of conditions; reaching end of
 422      * file before {@code n} bytes have been skipped is only one
 423      * possibility. This method never throws an {@code EOFException}.
 424      * The actual number of bytes skipped is returned.  If {@code n}
 425      * is negative, no bytes are skipped.
 426      *
 427      * @param      n   the number of bytes to be skipped.
 428      * @return     the actual number of bytes skipped.
 429      * @exception  IOException  if an I/O error occurs.
 430      */
 431     public int skipBytes(int n) throws IOException {
 432         long pos;
 433         long len;
 434         long newpos;
 435 
 436         if (n <= 0) {
 437             return 0;
 438         }
 439         pos = getFilePointer();
 440         len = length();
 441         newpos = pos + n;
 442         if (newpos > len) {
 443             newpos = len;
 444         }
 445         seek(newpos);
 446 
 447         /* return the actual number of bytes skipped */
 448         return (int) (newpos - pos);
 449     }
 450 
 451     // 'Write' primitives
 452 
 453     /**
 454      * Writes the specified byte to this file. The write starts at
 455      * the current file pointer.
 456      *
 457      * @param      b   the {@code byte} to be written.
 458      * @exception  IOException  if an I/O error occurs.
 459      */
 460     public native void write(int b) throws IOException;
 461 
 462     /**
 463      * Writes a sub array as a sequence of bytes.
 464      * @param b the data to be written
 465 
 466      * @param off the start offset in the data
 467      * @param len the number of bytes that are written
 468      * @exception IOException If an I/O error has occurred.
 469      */
 470     private native void writeBytes(byte b[], int off, int len) throws IOException;
 471 
 472     /**
 473      * Writes {@code b.length} bytes from the specified byte array
 474      * to this file, starting at the current file pointer.
 475      *
 476      * @param      b   the data.
 477      * @exception  IOException  if an I/O error occurs.
 478      */
 479     public void write(byte b[]) throws IOException {
 480         writeBytes(b, 0, b.length);
 481     }
 482 
 483     /**
 484      * Writes {@code len} bytes from the specified byte array
 485      * starting at offset {@code off} to this file.
 486      *
 487      * @param      b     the data.
 488      * @param      off   the start offset in the data.
 489      * @param      len   the number of bytes to write.
 490      * @exception  IOException  if an I/O error occurs.
 491      */
 492     public void write(byte b[], int off, int len) throws IOException {
 493         writeBytes(b, off, len);
 494     }
 495 
 496     // 'Random access' stuff
 497 
 498     /**
 499      * Returns the current offset in this file.
 500      *
 501      * @return     the offset from the beginning of the file, in bytes,
 502      *             at which the next read or write occurs.
 503      * @exception  IOException  if an I/O error occurs.
 504      */
 505     public native long getFilePointer() throws IOException;
 506 
 507     /**
 508      * Sets the file-pointer offset, measured from the beginning of this
 509      * file, at which the next read or write occurs.  The offset may be
 510      * set beyond the end of the file. Setting the offset beyond the end
 511      * of the file does not change the file length.  The file length will
 512      * change only by writing after the offset has been set beyond the end
 513      * of the file.
 514      *
 515      * @param      pos   the offset position, measured in bytes from the
 516      *                   beginning of the file, at which to set the file
 517      *                   pointer.
 518      * @exception  IOException  if {@code pos} is less than
 519      *                          {@code 0} or if an I/O error occurs.
 520      */
 521     public void seek(long pos) throws IOException {
 522         if (pos < 0) {
 523             throw new IOException("Negative seek offset");
 524         } else {
 525             seek0(pos);
 526         }
 527     }
 528 
 529     private native void seek0(long pos) throws IOException;
 530 
 531     /**
 532      * Returns the length of this file.
 533      *
 534      * @return     the length of this file, measured in bytes.
 535      * @exception  IOException  if an I/O error occurs.
 536      */
 537     public native long length() throws IOException;
 538 
 539     /**
 540      * Sets the length of this file.
 541      *
 542      * <p> If the present length of the file as returned by the
 543      * {@code length} method is greater than the {@code newLength}
 544      * argument then the file will be truncated.  In this case, if the file
 545      * offset as returned by the {@code getFilePointer} method is greater
 546      * than {@code newLength} then after this method returns the offset
 547      * will be equal to {@code newLength}.
 548      *
 549      * <p> If the present length of the file as returned by the
 550      * {@code length} method is smaller than the {@code newLength}
 551      * argument then the file will be extended.  In this case, the contents of
 552      * the extended portion of the file are not defined.
 553      *
 554      * @param      newLength    The desired length of the file
 555      * @exception  IOException  If an I/O error occurs
 556      * @since      1.2
 557      */
 558     public native void setLength(long newLength) throws IOException;
 559 
 560     /**
 561      * Closes this random access file stream and releases any system
 562      * resources associated with the stream. A closed random access
 563      * file cannot perform input or output operations and cannot be
 564      * reopened.
 565      *
 566      * <p> If this file has an associated channel then the channel is closed
 567      * as well.
 568      *
 569      * @exception  IOException  if an I/O error occurs.
 570      *
 571      * @revised 1.4
 572      * @spec JSR-51
 573      */
 574     public void close() throws IOException {
 575         synchronized (closeLock) {
 576             if (closed) {
 577                 return;
 578             }
 579             closed = true;
 580         }
 581         if (channel != null) {
 582             channel.close();
 583         }
 584 
 585         fd.closeAll(new Closeable() {
 586             public void close() throws IOException {
 587                close0();
 588            }
 589         });
 590     }
 591 
 592     //
 593     //  Some "reading/writing Java data types" methods stolen from
 594     //  DataInputStream and DataOutputStream.
 595     //
 596 
 597     /**
 598      * Reads a {@code boolean} from this file. This method reads a
 599      * single byte from the file, starting at the current file pointer.
 600      * A value of {@code 0} represents
 601      * {@code false}. Any other value represents {@code true}.
 602      * This method blocks until the byte is read, the end of the stream
 603      * is detected, or an exception is thrown.
 604      *
 605      * @return     the {@code boolean} value read.
 606      * @exception  EOFException  if this file has reached the end.
 607      * @exception  IOException   if an I/O error occurs.
 608      */
 609     public final boolean readBoolean() throws IOException {
 610         int ch = this.read();
 611         if (ch < 0)
 612             throw new EOFException();
 613         return (ch != 0);
 614     }
 615 
 616     /**
 617      * Reads a signed eight-bit value from this file. This method reads a
 618      * byte from the file, starting from the current file pointer.
 619      * If the byte read is {@code b}, where
 620      * <code>0&nbsp;&lt;=&nbsp;b&nbsp;&lt;=&nbsp;255</code>,
 621      * then the result is:
 622      * <blockquote><pre>
 623      *     (byte)(b)
 624      * </pre></blockquote>
 625      * <p>
 626      * This method blocks until the byte is read, the end of the stream
 627      * is detected, or an exception is thrown.
 628      *
 629      * @return     the next byte of this file as a signed eight-bit
 630      *             {@code byte}.
 631      * @exception  EOFException  if this file has reached the end.
 632      * @exception  IOException   if an I/O error occurs.
 633      */
 634     public final byte readByte() throws IOException {
 635         int ch = this.read();
 636         if (ch < 0)
 637             throw new EOFException();
 638         return (byte)(ch);
 639     }
 640 
 641     /**
 642      * Reads an unsigned eight-bit number from this file. This method reads
 643      * a byte from this file, starting at the current file pointer,
 644      * and returns that byte.
 645      * <p>
 646      * This method blocks until the byte is read, the end of the stream
 647      * is detected, or an exception is thrown.
 648      *
 649      * @return     the next byte of this file, interpreted as an unsigned
 650      *             eight-bit number.
 651      * @exception  EOFException  if this file has reached the end.
 652      * @exception  IOException   if an I/O error occurs.
 653      */
 654     public final int readUnsignedByte() throws IOException {
 655         int ch = this.read();
 656         if (ch < 0)
 657             throw new EOFException();
 658         return ch;
 659     }
 660 
 661     /**
 662      * Reads a signed 16-bit number from this file. The method reads two
 663      * bytes from this file, starting at the current file pointer.
 664      * If the two bytes read, in order, are
 665      * {@code b1} and {@code b2}, where each of the two values is
 666      * between {@code 0} and {@code 255}, inclusive, then the
 667      * result is equal to:
 668      * <blockquote><pre>
 669      *     (short)((b1 &lt;&lt; 8) | b2)
 670      * </pre></blockquote>
 671      * <p>
 672      * This method blocks until the two bytes are read, the end of the
 673      * stream is detected, or an exception is thrown.
 674      *
 675      * @return     the next two bytes of this file, interpreted as a signed
 676      *             16-bit number.
 677      * @exception  EOFException  if this file reaches the end before reading
 678      *               two bytes.
 679      * @exception  IOException   if an I/O error occurs.
 680      */
 681     public final short readShort() throws IOException {
 682         int ch1 = this.read();
 683         int ch2 = this.read();
 684         if ((ch1 | ch2) < 0)
 685             throw new EOFException();
 686         return (short)((ch1 << 8) + (ch2 << 0));
 687     }
 688 
 689     /**
 690      * Reads an unsigned 16-bit number from this file. This method reads
 691      * two bytes from the file, starting at the current file pointer.
 692      * If the bytes read, in order, are
 693      * {@code b1} and {@code b2}, where
 694      * <code>0&nbsp;&lt;=&nbsp;b1, b2&nbsp;&lt;=&nbsp;255</code>,
 695      * then the result is equal to:
 696      * <blockquote><pre>
 697      *     (b1 &lt;&lt; 8) | b2
 698      * </pre></blockquote>
 699      * <p>
 700      * This method blocks until the two bytes are read, the end of the
 701      * stream is detected, or an exception is thrown.
 702      *
 703      * @return     the next two bytes of this file, interpreted as an unsigned
 704      *             16-bit integer.
 705      * @exception  EOFException  if this file reaches the end before reading
 706      *               two bytes.
 707      * @exception  IOException   if an I/O error occurs.
 708      */
 709     public final int readUnsignedShort() throws IOException {
 710         int ch1 = this.read();
 711         int ch2 = this.read();
 712         if ((ch1 | ch2) < 0)
 713             throw new EOFException();
 714         return (ch1 << 8) + (ch2 << 0);
 715     }
 716 
 717     /**
 718      * Reads a character from this file. This method reads two
 719      * bytes from the file, starting at the current file pointer.
 720      * If the bytes read, in order, are
 721      * {@code b1} and {@code b2}, where
 722      * <code>0&nbsp;&lt;=&nbsp;b1,&nbsp;b2&nbsp;&lt;=&nbsp;255</code>,
 723      * then the result is equal to:
 724      * <blockquote><pre>
 725      *     (char)((b1 &lt;&lt; 8) | b2)
 726      * </pre></blockquote>
 727      * <p>
 728      * This method blocks until the two bytes are read, the end of the
 729      * stream is detected, or an exception is thrown.
 730      *
 731      * @return     the next two bytes of this file, interpreted as a
 732      *                  {@code char}.
 733      * @exception  EOFException  if this file reaches the end before reading
 734      *               two bytes.
 735      * @exception  IOException   if an I/O error occurs.
 736      */
 737     public final char readChar() throws IOException {
 738         int ch1 = this.read();
 739         int ch2 = this.read();
 740         if ((ch1 | ch2) < 0)
 741             throw new EOFException();
 742         return (char)((ch1 << 8) + (ch2 << 0));
 743     }
 744 
 745     /**
 746      * Reads a signed 32-bit integer from this file. This method reads 4
 747      * bytes from the file, starting at the current file pointer.
 748      * If the bytes read, in order, are {@code b1},
 749      * {@code b2}, {@code b3}, and {@code b4}, where
 750      * <code>0&nbsp;&lt;=&nbsp;b1, b2, b3, b4&nbsp;&lt;=&nbsp;255</code>,
 751      * then the result is equal to:
 752      * <blockquote><pre>
 753      *     (b1 &lt;&lt; 24) | (b2 &lt;&lt; 16) + (b3 &lt;&lt; 8) + b4
 754      * </pre></blockquote>
 755      * <p>
 756      * This method blocks until the four bytes are read, the end of the
 757      * stream is detected, or an exception is thrown.
 758      *
 759      * @return     the next four bytes of this file, interpreted as an
 760      *             {@code int}.
 761      * @exception  EOFException  if this file reaches the end before reading
 762      *               four bytes.
 763      * @exception  IOException   if an I/O error occurs.
 764      */
 765     public final int readInt() throws IOException {
 766         int ch1 = this.read();
 767         int ch2 = this.read();
 768         int ch3 = this.read();
 769         int ch4 = this.read();
 770         if ((ch1 | ch2 | ch3 | ch4) < 0)
 771             throw new EOFException();
 772         return ((ch1 << 24) + (ch2 << 16) + (ch3 << 8) + (ch4 << 0));
 773     }
 774 
 775     /**
 776      * Reads a signed 64-bit integer from this file. This method reads eight
 777      * bytes from the file, starting at the current file pointer.
 778      * If the bytes read, in order, are
 779      * {@code b1}, {@code b2}, {@code b3},
 780      * {@code b4}, {@code b5}, {@code b6},
 781      * {@code b7}, and {@code b8,} where:
 782      * <blockquote><pre>
 783      *     0 &lt;= b1, b2, b3, b4, b5, b6, b7, b8 &lt;=255,
 784      * </pre></blockquote>
 785      * <p>
 786      * then the result is equal to:
 787      * <blockquote><pre>
 788      *     ((long)b1 &lt;&lt; 56) + ((long)b2 &lt;&lt; 48)
 789      *     + ((long)b3 &lt;&lt; 40) + ((long)b4 &lt;&lt; 32)
 790      *     + ((long)b5 &lt;&lt; 24) + ((long)b6 &lt;&lt; 16)
 791      *     + ((long)b7 &lt;&lt; 8) + b8
 792      * </pre></blockquote>
 793      * <p>
 794      * This method blocks until the eight bytes are read, the end of the
 795      * stream is detected, or an exception is thrown.
 796      *
 797      * @return     the next eight bytes of this file, interpreted as a
 798      *             {@code long}.
 799      * @exception  EOFException  if this file reaches the end before reading
 800      *               eight bytes.
 801      * @exception  IOException   if an I/O error occurs.
 802      */
 803     public final long readLong() throws IOException {
 804         return ((long)(readInt()) << 32) + (readInt() & 0xFFFFFFFFL);
 805     }
 806 
 807     /**
 808      * Reads a {@code float} from this file. This method reads an
 809      * {@code int} value, starting at the current file pointer,
 810      * as if by the {@code readInt} method
 811      * and then converts that {@code int} to a {@code float}
 812      * using the {@code intBitsToFloat} method in class
 813      * {@code Float}.
 814      * <p>
 815      * This method blocks until the four bytes are read, the end of the
 816      * stream is detected, or an exception is thrown.
 817      *
 818      * @return     the next four bytes of this file, interpreted as a
 819      *             {@code float}.
 820      * @exception  EOFException  if this file reaches the end before reading
 821      *             four bytes.
 822      * @exception  IOException   if an I/O error occurs.
 823      * @see        java.io.RandomAccessFile#readInt()
 824      * @see        java.lang.Float#intBitsToFloat(int)
 825      */
 826     public final float readFloat() throws IOException {
 827         return Float.intBitsToFloat(readInt());
 828     }
 829 
 830     /**
 831      * Reads a {@code double} from this file. This method reads a
 832      * {@code long} value, starting at the current file pointer,
 833      * as if by the {@code readLong} method
 834      * and then converts that {@code long} to a {@code double}
 835      * using the {@code longBitsToDouble} method in
 836      * class {@code Double}.
 837      * <p>
 838      * This method blocks until the eight bytes are read, the end of the
 839      * stream is detected, or an exception is thrown.
 840      *
 841      * @return     the next eight bytes of this file, interpreted as a
 842      *             {@code double}.
 843      * @exception  EOFException  if this file reaches the end before reading
 844      *             eight bytes.
 845      * @exception  IOException   if an I/O error occurs.
 846      * @see        java.io.RandomAccessFile#readLong()
 847      * @see        java.lang.Double#longBitsToDouble(long)
 848      */
 849     public final double readDouble() throws IOException {
 850         return Double.longBitsToDouble(readLong());
 851     }
 852 
 853     /**
 854      * Reads the next line of text from this file.  This method successively
 855      * reads bytes from the file, starting at the current file pointer,
 856      * until it reaches a line terminator or the end
 857      * of the file.  Each byte is converted into a character by taking the
 858      * byte's value for the lower eight bits of the character and setting the
 859      * high eight bits of the character to zero.  This method does not,
 860      * therefore, support the full Unicode character set.
 861      *
 862      * <p> A line of text is terminated by a carriage-return character
 863      * ({@code '\u005Cr'}), a newline character ({@code '\u005Cn'}), a
 864      * carriage-return character immediately followed by a newline character,
 865      * or the end of the file.  Line-terminating characters are discarded and
 866      * are not included as part of the string returned.
 867      *
 868      * <p> This method blocks until a newline character is read, a carriage
 869      * return and the byte following it are read (to see if it is a newline),
 870      * the end of the file is reached, or an exception is thrown.
 871      *
 872      * @return     the next line of text from this file, or null if end
 873      *             of file is encountered before even one byte is read.
 874      * @exception  IOException  if an I/O error occurs.
 875      */
 876 
 877     public final String readLine() throws IOException {
 878         StringBuffer input = new StringBuffer();
 879         int c = -1;
 880         boolean eol = false;
 881 
 882         while (!eol) {
 883             switch (c = read()) {
 884             case -1:
 885             case '\n':
 886                 eol = true;
 887                 break;
 888             case '\r':
 889                 eol = true;
 890                 long cur = getFilePointer();
 891                 if ((read()) != '\n') {
 892                     seek(cur);
 893                 }
 894                 break;
 895             default:
 896                 input.append((char)c);
 897                 break;
 898             }
 899         }
 900 
 901         if ((c == -1) && (input.length() == 0)) {
 902             return null;
 903         }
 904         return input.toString();
 905     }
 906 
 907     /**
 908      * Reads in a string from this file. The string has been encoded
 909      * using a
 910      * <a href="DataInput.html#modified-utf-8">modified UTF-8</a>
 911      * format.
 912      * <p>
 913      * The first two bytes are read, starting from the current file
 914      * pointer, as if by
 915      * {@code readUnsignedShort}. This value gives the number of
 916      * following bytes that are in the encoded string, not
 917      * the length of the resulting string. The following bytes are then
 918      * interpreted as bytes encoding characters in the modified UTF-8 format
 919      * and are converted into characters.
 920      * <p>
 921      * This method blocks until all the bytes are read, the end of the
 922      * stream is detected, or an exception is thrown.
 923      *
 924      * @return     a Unicode string.
 925      * @exception  EOFException            if this file reaches the end before
 926      *               reading all the bytes.
 927      * @exception  IOException             if an I/O error occurs.
 928      * @exception  UTFDataFormatException  if the bytes do not represent
 929      *               valid modified UTF-8 encoding of a Unicode string.
 930      * @see        java.io.RandomAccessFile#readUnsignedShort()
 931      */
 932     public final String readUTF() throws IOException {
 933         return DataInputStream.readUTF(this);
 934     }
 935 
 936     /**
 937      * Writes a {@code boolean} to the file as a one-byte value. The
 938      * value {@code true} is written out as the value
 939      * {@code (byte)1}; the value {@code false} is written out
 940      * as the value {@code (byte)0}. The write starts at
 941      * the current position of the file pointer.
 942      *
 943      * @param      v   a {@code boolean} value to be written.
 944      * @exception  IOException  if an I/O error occurs.
 945      */
 946     public final void writeBoolean(boolean v) throws IOException {
 947         write(v ? 1 : 0);
 948         //written++;
 949     }
 950 
 951     /**
 952      * Writes a {@code byte} to the file as a one-byte value. The
 953      * write starts at the current position of the file pointer.
 954      *
 955      * @param      v   a {@code byte} value to be written.
 956      * @exception  IOException  if an I/O error occurs.
 957      */
 958     public final void writeByte(int v) throws IOException {
 959         write(v);
 960         //written++;
 961     }
 962 
 963     /**
 964      * Writes a {@code short} to the file as two bytes, high byte first.
 965      * The write starts at the current position of the file pointer.
 966      *
 967      * @param      v   a {@code short} to be written.
 968      * @exception  IOException  if an I/O error occurs.
 969      */
 970     public final void writeShort(int v) throws IOException {
 971         write((v >>> 8) & 0xFF);
 972         write((v >>> 0) & 0xFF);
 973         //written += 2;
 974     }
 975 
 976     /**
 977      * Writes a {@code char} to the file as a two-byte value, high
 978      * byte first. The write starts at the current position of the
 979      * file pointer.
 980      *
 981      * @param      v   a {@code char} value to be written.
 982      * @exception  IOException  if an I/O error occurs.
 983      */
 984     public final void writeChar(int v) throws IOException {
 985         write((v >>> 8) & 0xFF);
 986         write((v >>> 0) & 0xFF);
 987         //written += 2;
 988     }
 989 
 990     /**
 991      * Writes an {@code int} to the file as four bytes, high byte first.
 992      * The write starts at the current position of the file pointer.
 993      *
 994      * @param      v   an {@code int} to be written.
 995      * @exception  IOException  if an I/O error occurs.
 996      */
 997     public final void writeInt(int v) throws IOException {
 998         write((v >>> 24) & 0xFF);
 999         write((v >>> 16) & 0xFF);
1000         write((v >>>  8) & 0xFF);
1001         write((v >>>  0) & 0xFF);
1002         //written += 4;
1003     }
1004 
1005     /**
1006      * Writes a {@code long} to the file as eight bytes, high byte first.
1007      * The write starts at the current position of the file pointer.
1008      *
1009      * @param      v   a {@code long} to be written.
1010      * @exception  IOException  if an I/O error occurs.
1011      */
1012     public final void writeLong(long v) throws IOException {
1013         write((int)(v >>> 56) & 0xFF);
1014         write((int)(v >>> 48) & 0xFF);
1015         write((int)(v >>> 40) & 0xFF);
1016         write((int)(v >>> 32) & 0xFF);
1017         write((int)(v >>> 24) & 0xFF);
1018         write((int)(v >>> 16) & 0xFF);
1019         write((int)(v >>>  8) & 0xFF);
1020         write((int)(v >>>  0) & 0xFF);
1021         //written += 8;
1022     }
1023 
1024     /**
1025      * Converts the float argument to an {@code int} using the
1026      * {@code floatToIntBits} method in class {@code Float},
1027      * and then writes that {@code int} value to the file as a
1028      * four-byte quantity, high byte first. The write starts at the
1029      * current position of the file pointer.
1030      *
1031      * @param      v   a {@code float} value to be written.
1032      * @exception  IOException  if an I/O error occurs.
1033      * @see        java.lang.Float#floatToIntBits(float)
1034      */
1035     public final void writeFloat(float v) throws IOException {
1036         writeInt(Float.floatToIntBits(v));
1037     }
1038 
1039     /**
1040      * Converts the double argument to a {@code long} using the
1041      * {@code doubleToLongBits} method in class {@code Double},
1042      * and then writes that {@code long} value to the file as an
1043      * eight-byte quantity, high byte first. The write starts at the current
1044      * position of the file pointer.
1045      *
1046      * @param      v   a {@code double} value to be written.
1047      * @exception  IOException  if an I/O error occurs.
1048      * @see        java.lang.Double#doubleToLongBits(double)
1049      */
1050     public final void writeDouble(double v) throws IOException {
1051         writeLong(Double.doubleToLongBits(v));
1052     }
1053 
1054     /**
1055      * Writes the string to the file as a sequence of bytes. Each
1056      * character in the string is written out, in sequence, by discarding
1057      * its high eight bits. The write starts at the current position of
1058      * the file pointer.
1059      *
1060      * @param      s   a string of bytes to be written.
1061      * @exception  IOException  if an I/O error occurs.
1062      */
1063     @SuppressWarnings("deprecation")
1064     public final void writeBytes(String s) throws IOException {
1065         int len = s.length();
1066         byte[] b = new byte[len];
1067         s.getBytes(0, len, b, 0);
1068         writeBytes(b, 0, len);
1069     }
1070 
1071     /**
1072      * Writes a string to the file as a sequence of characters. Each
1073      * character is written to the data output stream as if by the
1074      * {@code writeChar} method. The write starts at the current
1075      * position of the file pointer.
1076      *
1077      * @param      s   a {@code String} value to be written.
1078      * @exception  IOException  if an I/O error occurs.
1079      * @see        java.io.RandomAccessFile#writeChar(int)
1080      */
1081     public final void writeChars(String s) throws IOException {
1082         int clen = s.length();
1083         int blen = 2*clen;
1084         byte[] b = new byte[blen];
1085         char[] c = new char[clen];
1086         s.getChars(0, clen, c, 0);
1087         for (int i = 0, j = 0; i < clen; i++) {
1088             b[j++] = (byte)(c[i] >>> 8);
1089             b[j++] = (byte)(c[i] >>> 0);
1090         }
1091         writeBytes(b, 0, blen);
1092     }
1093 
1094     /**
1095      * Writes a string to the file using
1096      * <a href="DataInput.html#modified-utf-8">modified UTF-8</a>
1097      * encoding in a machine-independent manner.
1098      * <p>
1099      * First, two bytes are written to the file, starting at the
1100      * current file pointer, as if by the
1101      * {@code writeShort} method giving the number of bytes to
1102      * follow. This value is the number of bytes actually written out,
1103      * not the length of the string. Following the length, each character
1104      * of the string is output, in sequence, using the modified UTF-8 encoding
1105      * for each character.
1106      *
1107      * @param      str   a string to be written.
1108      * @exception  IOException  if an I/O error occurs.
1109      */
1110     public final void writeUTF(String str) throws IOException {
1111         DataOutputStream.writeUTF(str, this);
1112     }
1113 
1114     private static native void initIDs();
1115 
1116     private native void close0() throws IOException;
1117 
1118     static {
1119         initIDs();
1120     }
1121 }