datainput.java

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  * It operates by reading eight bytes from the stream and converting them to 
  * a single Java <code>long</code>.  The bytes are stored most
  * significant byte first (i.e., "big endian") regardless of the native
  * host byte ordering. 
  * <p>
  * As an example, if <code>byte1</code> through <code>byte8</code> represent
  * the first eight bytes read from the stream, they will be
  * transformed to an <code>long</code> in the following manner:
  * <p>
  * <code>(long)((byte1 << 56) + (byte2 << 48) + (byte3 << 40) + 
  * (byte4 << 32) + (byte5 << 24) + (byte6 << 16) + (byte7 << 8) + byte9))
  * </code>
  * <p>
  * The value returned is in the range of -9223372036854775808 to
  * 9223372036854775807.
  * <p>
  * This method can read an <code>long</code> written by an object implementing
  * the <code>writeLong()</code> method in the <code>DataOutput</code>
  * interface.
  *
  * @return The <code>long</code> value read
  *
  * @exception EOFException If end of file is reached before reading the long
  * @exception IOException If any other error occurs
  *
  * @see DataOutput
  */
long
readLong() throws EOFException, IOException;

/*************************************************************************/

/**
  * This method reads a Java float value from an input stream.  It operates
  * by first reading an <code>int</code> value from the stream by calling the
  * <code>readInt()</code> method in this interface, then converts that
  * <code>int</code> to a <code>float</code> using the
  * <code>intBitsToFloat</code> method in the class
  * <code>java.lang.Float</code>.
  * <p>
  * This method can read a <code>float</code> written by an object implementing
  * the <code>writeFloat()</code> method in the <code>DataOutput</code>
  * interface.
  *
  * @return The <code>float</code> value read
  *
  * @exception EOFException If end of file is reached before reading the float
  * @exception IOException If any other error occurs
  *
  * @see java.lang.Float
  * @see DataOutput
  */
float
readFloat() throws EOFException, IOException;

/*************************************************************************/

/**
  * This method reads a Java double value from an input stream.  It operates
  * by first reading a <code>long</code> value from the stream by calling the
  * <code>readLong()</code> method in this interface, then converts that
  * <code>long</code> to a <code>double</code> using the
  * <code>longBitsToDouble</code> method in the class
  * <code>java.lang.Double</code>.
  * <p>
  * This method can read a <code>double</code> written by an object
  * implementing the <code>writeDouble()</code> method in the
  * <code>DataOutput</code> interface.
  *
  * @return The <code>double</code> value read
  *
  * @exception EOFException If end of file is reached before reading the double
  * @exception IOException If any other error occurs
  *
  * @see java.lang.Double
  * @see DataOutput
  */
double
readDouble() throws EOFException, IOException;

/*************************************************************************/

/**
  * This method reads the next line of text data from an input stream.
  * It operates by reading bytes and converting those bytes to <code>char</code>
  * values by treating the byte read as the low eight bits of the
  * <code>char</code> and using 0 as the high eight bits.  Because of this,
  * it does not support the full 16-bit Unicode character set.
  * <P>
  * The reading of bytes ends when either the end of file or a line terminator
  * is encountered.  The bytes read are then returned as a <code>String</code>.
  * A line terminator is a byte sequence consisting of either 
  * <code>\r</code>, <code>\n</code> or <code>\r\n</code>.  These termination
  * charaters are discarded and are not returned as part of the string.
  * <p>
  * This method can read data that was written by an object implementing the
  * <code>writeLine()</code> method in <code>DataOutput</code>.
  *
  * @return The line read as a <code>String</code>
  *
  * @exception IOException If an error occurs
  *
  * @see DataOutput
  */
String
readLine() throws IOException;

/*************************************************************************/

/**
  * This method reads a <code>String</code> from an input stream that is
  * encoded in a modified UTF-8 format.  This format has a leading two byte
  * sequence that contains the remaining number of bytes to read.  This two byte
  * sequence is read using the <code>readUnsignedShort()</code> method of this
  * interface.
  *
  * After the number of remaining bytes have been determined, these bytes
  * are read an transformed into <code>char</code> values.  These
  * <code>char</code> values are encoded in the stream using either a one, two,
  * or three byte format.
  * The particular format in use can be determined by examining the first
  * byte read.  
  * <p>
  * If the first byte has a high order bit of 0, then
  * that character consists on only one byte.  This character value consists
  * of seven bits that are at positions 0 through 6 of the byte.  As an
  * example, if <code>byte1</code> is the byte read from the stream, it would
  * be converted to a <code>char</code> like so:
  * <p>
  * <code>(char)byte1</code>
  * <p>
  * If the first byte has 110 as its high order bits, then the 
  * character consists of two bytes.  The bits that make up the character
  * value are in positions 0 through 4 of the first byte and bit positions
  * 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 1110 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 10 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:
  *
  * <code>
  * (char)(((byte1 & 0x0F) << 12) + ((byte2 & 0x3F) + (byte3 & 0x3F))
  * </code>
  *
  * 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>\<llll>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>.
  * 
  * @returns 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
  */
String
readUTF() throws EOFException, UTFDataFormatException, IOException;

/*************************************************************************/

/**
  * This method reads raw bytes into the passed array until the array is
  * full.  Note that this method blocks until the data is available and
  * throws an exception if there is not enough data left in the stream to
  * fill the buffer
  *
  * @param buf The buffer into which to read the data
  *
  * @exception EOFException If end of file is reached before filling the buffer
  * @exception IOException If any other error occurs
  */
void
readFully(byte[] buf) throws EOFException, IOException;

/*************************************************************************/

/**
  * This method reads raw bytes into the passed array <code>buf</code> starting
  * <code>offset</code> bytes into the buffer.  The number of bytes read will be
  * exactly <code>len</code>.  Note that this method blocks until the data is 
  * available and * throws an exception if there is not enough data left in 
  * the stream to read <code>len</code> bytes.
  *
  * @param buf The buffer into which to read the data
  * @param offset The offset into the buffer to start storing data
  * @param len The number of bytes to read into the buffer
  *
  * @exception EOFException If end of file is reached before filling the buffer
  * @exception IOException If any other error occurs
  */
void
readFully(byte[] buf, int offset, int len) throws EOFException, IOException;

/*************************************************************************/

/**
  * This method skips and discards the specified number of bytes in an
  * input stream
  *
  * @param num_bytes The number of bytes to skip
  *
  * @return The number of bytes actually skipped, which will always be
  *         <code>num_bytes</code>
  *
  * @exception EOFException If end of file is reached before all bytes can be
  *                         skipped
  * @exception IOException If any other error occurs
  */
int
skipBytes(int n) throws EOFException, IOException;

} // interface DataInput