randomaccessfile.java

gcc的组建

   * 0 through 5 of the second byte.  (The second byte should have 
   * 10 as its high order bits).  These values are in most significant
   * byte first (i.e., "big endian") order.
   * <p>
   * As an example, if <code>byte1</code> and <code>byte2</code> 
   * are the first two bytes
   * read respectively, and the high order bits of them match the patterns
   * which indicate a two byte character encoding, then they would be
   * converted to a Java <code>char</code> like so:
   * <p>
   * <code>(char)(((byte1 & 0x1F) << 6) | (byte2 & 0x3F))</code>
   * <p>
   * If the first byte has a <code>1110</code> as its high order bits, then the
   * character consists of three bytes.  The bits that make up the character
   * value are in positions 0 through 3 of the first byte and bit positions
   * 0 through 5 of the other two bytes.  (The second and third bytes should
   * have <code>10</code> as their high order bits).  These values are in most
   * significant byte first (i.e., "big endian") order.
   * <p>
   * As an example, if <code>byte1</code> <code>byte2</code> 
   * and <code>byte3</code> are the
   * three bytes read, and the high order bits of them match the patterns
   * which indicate a three byte character encoding, then they would be
   * converted to a Java <code>char</code> like so:
   * <p>
   * <code>(char)(((byte1 & 0x0F) << 12) | ((byte2 & 0x3F) << 6) | 
   * (byte3 & 0x3F))</code>
   * <p>
   * Note that all characters are encoded in the method that requires the
   * fewest number of bytes with the exception of the character with the
   * value of <code>&#92;u0000</code> which is encoded as two bytes.  This is 
   * a  modification of the UTF standard used to prevent C language style
   * <code>NUL</code> values from appearing in the byte stream.
   * <p>
   * This method can read data that was written by an object implementing the
   * <code>writeUTF()</code> method in <code>DataOutput</code>
   * 
   * @return The <code>String</code> read
   *
   * @exception EOFException If end of file is reached before reading the 
   * String
   * @exception UTFDataFormatException If the data is not in UTF-8 format
   * @exception IOException If any other error occurs
   *
   * @see DataOutput
   */
  public final String readUTF () throws IOException
  {
    return in.readUTF();
  }

  /**
   * This method sets the current file position to the specified offset 
   * from the beginning of the file.  Note that some operating systems will
   * allow the file pointer to be set past the current end of the file.
   *
   * @param pos The offset from the beginning of the file at which to set 
   * the file pointer
   *
   * @exception IOException If an error occurs
   */
  public void seek (long pos) throws IOException
  {
    ch.position(pos);
  }

  /**
   * This method attempts to skip and discard the specified number of bytes 
   * in the input stream.  It may actually skip fewer bytes than requested. 
   * The actual number of bytes skipped is returned.  This method will not
   * skip any bytes if passed a negative number of bytes to skip.
   *
   * @param numBytes The requested number of bytes to skip.
   *
   * @return The number of bytes actually skipped.
   *
   * @exception IOException If an error occurs.
   */
  public int skipBytes (int numBytes) throws IOException
  {
    if (numBytes < 0)
      throw new IllegalArgumentException ("Can't skip negative bytes: " +
                                          numBytes);
    
    if (numBytes == 0)
      return 0;
    
    long oldPos = ch.position();
    long newPos = oldPos + numBytes;
    long size = ch.size();
    if (newPos > size)
      newPos = size;
    ch.position(newPos);
    return (int) (ch.position() - oldPos);
  }

  /**
   * This method writes a single byte of data to the file. The file must
   * be open for read-write in order for this operation to succeed.
   *
   * @param oneByte The byte of data to write, passed as an int.
   *
   * @exception IOException If an error occurs
   */
  public void write (int oneByte) throws IOException
  {
    out.write(oneByte);
  }

  /**
   * This method writes all the bytes in the specified array to the file.
   * The file must be open read-write in order for this operation to succeed.
   *
   * @param buffer The array of bytes to write to the file
   */
  public void write (byte[] buffer) throws IOException
  {
    out.write(buffer);
  }

  /**
   * This method writes <code>len</code> bytes to the file from the specified
   * array starting at index <code>offset</code> into the array.
   *
   * @param buffer The array of bytes to write to the file
   * @param offset The index into the array to start writing file
   * @param len The number of bytes to write
   *
   * @exception IOException If an error occurs
   */
  public void write (byte[] buffer, int offset, int len) throws IOException
  {
    out.write (buffer, offset, len);
  }

  /**
   * This method writes a Java <code>boolean</code> to the underlying output 
   * stream. For a value of <code>true</code>, 1 is written to the stream.
   * For a value of <code>false</code>, 0 is written.
   *
   * @param val The <code>boolean</code> value to write to the stream
   *
   * @exception IOException If an error occurs
   */
  public final void writeBoolean (boolean val) throws IOException
  {
    out.writeBoolean(val);
  }

  /**
   * This method writes a Java <code>byte</code> value to the underlying
   * output stream.
   *
   * @param val The <code>byte</code> to write to the stream, passed 
   * as an <code>int</code>.
   *
   * @exception IOException If an error occurs
   */
  public final void writeByte (int val) throws IOException
  {
    out.writeByte(val);
  }

  /**
   * This method writes a Java <code>short</code> to the stream, high byte
   * first.  This method requires two bytes to encode the value.
   *
   * @param val The <code>short</code> value to write to the stream, 
   * passed as an <code>int</code>.
   *
   * @exception IOException If an error occurs
   */
  public final void writeShort (int val) throws IOException
  {
    out.writeShort(val);
  }

  /**
   * This method writes a single <code>char</code> value to the stream,
   * high byte first.
   *
   * @param val The <code>char</code> value to write, passed as 
   * an <code>int</code>.
   *
   * @exception IOException If an error occurs
   */
  public final void writeChar (int val) throws IOException
  {
    out.writeChar(val);
  }

  /**
   * This method writes a Java <code>int</code> to the stream, high bytes
   * first.  This method requires four bytes to encode the value.
   *
   * @param val The <code>int</code> value to write to the stream.
   *
   * @exception IOException If an error occurs
   */
  public final void writeInt (int val) throws IOException
  {
    out.writeInt(val);
  }

  /**
   * This method writes a Java <code>long</code> to the stream, high bytes
   * first.  This method requires eight bytes to encode the value.
   *
   * @param val The <code>long</code> value to write to the stream.
   *
   * @exception IOException If an error occurs
   */
  public final void writeLong (long val) throws IOException
  {
    out.writeLong(val);
  }

  /**
   * This method writes a Java <code>float</code> value to the stream.  This
   * value is written by first calling the method 
   * <code>Float.floatToIntBits</code>
   * to retrieve an <code>int</code> representing the floating point number,
   * then writing this <code>int</code> value to the stream exactly the same
   * as the <code>writeInt()</code> method does.
   *
   * @param val The floating point number to write to the stream.
   *
   * @exception IOException If an error occurs
   *
   * @see #writeInt(int)
   */
  public final void writeFloat (float val) throws IOException
  {
    out.writeFloat(val);
  }

  /**
   * This method writes a Java <code>double</code> value to the stream.  This
   * value is written by first calling the method 
   * <code>Double.doubleToLongBits</code>
   * to retrieve an <code>long</code> representing the floating point number,
   * then writing this <code>long</code> value to the stream exactly the same
   * as the <code>writeLong()</code> method does.
   *
   * @param val The double precision floating point number to write to the 
   * stream.
   *
   * @exception IOException If an error occurs
   *
   * @see #writeLong(long)
   */
  public final void writeDouble (double val) throws IOException
  {
    out.writeDouble(val);
  }

  /**
   * This method writes all the bytes in a <code>String</code> out to the
   * stream.  One byte is written for each character in the <code>String</code>.
   * The high eight bits of each character are discarded.
   *
   * @param val The <code>String</code> to write to the stream
   *
   * @exception IOException If an error occurs
   */
  public final void writeBytes (String val) throws IOException
  {
    out.writeBytes(val);
  }
  
  /**
   * This method writes all the characters in a <code>String</code> to the
   * stream.  There will be two bytes for each character value.  The high
   * byte of the character will be written first.
   *
   * @param val The <code>String</code> to write to the stream.
   *
   * @exception IOException If an error occurs
   */
  public final void writeChars (String val) throws IOException
  {
    out.writeChars(val);
  }
  
  /**
   * This method writes a Java <code>String</code> to the stream in a modified
   * UTF-8 format.  First, two bytes are written to the stream indicating the
   * number of bytes to follow.  Note that this is the number of bytes in the
   * encoded <code>String</code> not the <code>String</code> length.  Next
   * come the encoded characters.  Each character in the <code>String</code>
   * is encoded as either one, two or three bytes.  For characters in the
   * range of <code>&#92;u0001</code> to <code>&#92;u007F</code>, 
   * one byte is used.  The character
   * value goes into bits 0-7 and bit eight is 0.  For characters in the range
   * of <code>&#92;u0080</code> to <code>&#92;u007FF</code>, two 
   * bytes are used.  Bits
   * 6-10 of the character value are encoded bits 0-4 of the first byte, with
   * the high bytes having a value of "110".  Bits 0-5 of the character value
   * are stored in bits 0-5 of the second byte, with the high bits set to
   * "10".  This type of encoding is also done for the null character
   * <code>&#92;u0000</code>.  This eliminates any C style NUL character values
   * in the output.  All remaining characters are stored as three bytes.
   * Bits 12-15 of the character value are stored in bits 0-3 of the first
   * byte.  The high bits of the first bytes are set to "1110".  Bits 6-11
   * of the character value are stored in bits 0-5 of the second byte.  The
   * high bits of the second byte are set to "10".  And bits 0-5 of the
   * character value are stored in bits 0-5 of byte three, with the high bits
   * of that byte set to "10".
   *
   * @param val The <code>String</code> to write to the output in UTF format
   *
   * @exception IOException If an error occurs
   */
  public final void writeUTF (String val) throws IOException
  {
    out.writeUTF(val);
  }
  
  /**
   * This method creates a java.nio.channels.FileChannel.
   * Nio does not allow one to create a file channel directly.
   * A file channel must be created by first creating an instance of
   * Input/Output/RandomAccessFile and invoking the getChannel() method on it.
   */
  public final synchronized FileChannel getChannel ()
  {
    return ch;
  }
}