https://openjdk.java.net/ 
/*
 * Copyright (c) 1995, 2019, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package java.io;


The DataInput interface provides for reading bytes from a binary stream and reconstructing from them data in any of the Java primitive types. There is also a facility for reconstructing a String from data in modified UTF-8
format.

 It is generally true of all the reading routines in this interface that if end of file is reached before the desired number of bytes has been read, an EOFException (which is a kind of IOException) is thrown. If any byte cannot be read for any reason other than end of file, an IOException other than EOFException is thrown. In particular, an IOException may be thrown if the input stream has been closed. 
Modified UTF-8



Implementations of the DataInput and DataOutput interfaces represent
Unicode strings in a format that is a slight modification of UTF-8.
(For information regarding the standard UTF-8 format, see section
3.9 Unicode Encoding Forms of The Unicode Standard, Version
4.0)

    

  • Characters in the range '\u005Cu0001' to '\u005Cu007F' are represented by a single byte. 
  • The null character '\u005Cu0000' and characters in the range '\u005Cu0080' to '\u005Cu07FF' are represented by a pair of bytes. 
  • Characters in the range '\u005Cu0800' to '\u005CuFFFF' are represented by three bytes. 

  

    Encoding of UTF-8 values
    
    

      Value
      Byte
      Bit Values
    

    

      
      
       7 
       6 
       5 
       4 
       3 
       2 
       1 
       0 
    

    
    

       \u005Cu0001 to \u005Cu007F 
       1 
      0
      bits 6-0
    

    

       \u005Cu0000,
 \u005Cu0080 to \u005Cu07FF 		
       1 
      1
      1
      0
      bits 10-6
    

    

      
       2 
      1
      0
      bits 5-0
    

    

       \u005Cu0800 to \u005CuFFFF 
       1 
      1
      1
      1
      0
      bits 15-12
    

    

      
       2 
      1
      0
      bits 11-6
    

    

      
       3 
      1
      0
      bits 5-0
    

    
  



The differences between this format and the
standard UTF-8 format are the following:

    

  • The null byte '\u005Cu0000' is encoded in 2-byte format rather than 1-byte, so that the encoded strings never have embedded nulls. 
  • Only the 1-byte, 2-byte, and 3-byte formats are used.

  • Supplementary characters
    are represented in the form of surrogate pairs.



Author: Frank Yellin
See Also:
Since:  1.0
/**
 * The {@code DataInput} interface provides
 * for reading bytes from a binary stream and
 * reconstructing from them data in any of
 * the Java primitive types. There is also
 * a
 * facility for reconstructing a {@code String}
 * from data in
 * <a href="#modified-utf-8">modified UTF-8</a>
 * format.
 * <p>
 * It is generally true of all the reading
 * routines in this interface that if end of
 * file is reached before the desired number
 * of bytes has been read, an {@code EOFException}
 * (which is a kind of {@code IOException})
 * is thrown. If any byte cannot be read for
 * any reason other than end of file, an {@code IOException}
 * other than {@code EOFException} is
 * thrown. In particular, an {@code IOException}
 * may be thrown if the input stream has been
 * closed.
 *
 * <h2><a id="modified-utf-8">Modified UTF-8</a></h2>
 * <p>
 * Implementations of the DataInput and DataOutput interfaces represent
 * Unicode strings in a format that is a slight modification of UTF-8.
 * (For information regarding the standard UTF-8 format, see section
 * <i>3.9 Unicode Encoding Forms</i> of <i>The Unicode Standard, Version
 * 4.0</i>)
 *
 * <ul>
 * <li>Characters in the range {@code '\u005Cu0001'} to
 *         {@code '\u005Cu007F'} are represented by a single byte.
 * <li>The null character {@code '\u005Cu0000'} and characters
 *         in the range {@code '\u005Cu0080'} to {@code '\u005Cu07FF'} are
 *         represented by a pair of bytes.
 * <li>Characters in the range {@code '\u005Cu0800'}
 *         to {@code '\u005CuFFFF'} are represented by three bytes.
 * </ul>
 *
 *   <table class="plain" style="margin-left:2em;">
 *     <caption>Encoding of UTF-8 values</caption>
 *     <thead>
 *     <tr>
 *       <th scope="col" rowspan="2">Value</th>
 *       <th scope="col" rowspan="2">Byte</th>
 *       <th scope="col" colspan="8" id="bit_a">Bit Values</th>
 *     </tr>
 *     <tr>
 *       <!-- Value -->
 *       <!-- Byte -->
 *       <th scope="col" style="width:3em"> 7 </th>
 *       <th scope="col" style="width:3em"> 6 </th>
 *       <th scope="col" style="width:3em"> 5 </th>
 *       <th scope="col" style="width:3em"> 4 </th>
 *       <th scope="col" style="width:3em"> 3 </th>
 *       <th scope="col" style="width:3em"> 2 </th>
 *       <th scope="col" style="width:3em"> 1 </th>
 *       <th scope="col" style="width:3em"> 0 </th>
 *     </thead>
 *     <tbody>
 *     <tr>
 *       <th scope="row" style="text-align:left; font-weight:normal">
 *         {@code \u005Cu0001} to {@code \u005Cu007F} </th>
 *       <th scope="row" style="font-weight:normal; text-align:center"> 1 </th>
 *       <td style="text-align:center">0
 *       <td colspan="7" style="text-align:right; padding-right:6em">bits 6-0
 *     </tr>
 *     <tr>
 *       <th scope="row" rowspan="2" style="text-align:left; font-weight:normal">
 *           {@code \u005Cu0000},<br>
 *           {@code \u005Cu0080} to {@code \u005Cu07FF} </th>
 *       <th scope="row" style="font-weight:normal; text-align:center"> 1 </th>
 *       <td style="text-align:center">1
 *       <td style="text-align:center">1
 *       <td style="text-align:center">0
 *       <td colspan="5" style="text-align:right; padding-right:6em">bits 10-6
 *     </tr>
 *     <tr>
 *       <!-- (value) -->
 *       <th scope="row" style="font-weight:normal; text-align:center"> 2 </th>
 *       <td style="text-align:center">1
 *       <td style="text-align:center">0
 *       <td colspan="6" style="text-align:right; padding-right:6em">bits 5-0
 *     </tr>
 *     <tr>
 *       <th scope="row" rowspan="3" style="text-align:left; font-weight:normal">
 *         {@code \u005Cu0800} to {@code \u005CuFFFF} </th>
 *       <th scope="row" style="font-weight:normal; text-align:center"> 1 </th>
 *       <td style="text-align:center">1
 *       <td style="text-align:center">1
 *       <td style="text-align:center">1
 *       <td style="text-align:center">0
 *       <td colspan="4" style="text-align:right; padding-right:6em">bits 15-12
 *     </tr>
 *     <tr>
 *       <!-- (value) -->
 *       <th scope="row" style="font-weight:normal; text-align:center"> 2 </th>
 *       <td style="text-align:center">1
 *       <td style="text-align:center">0
 *       <td colspan="6" style="text-align:right; padding-right:6em">bits 11-6
 *     </tr>
 *     <tr>
 *       <!-- (value) -->
 *       <th scope="row" style="font-weight:normal; text-align:center"> 3 </th>
 *       <td style="text-align:center">1
 *       <td style="text-align:center">0
 *       <td colspan="6" style="text-align:right; padding-right:6em">bits 5-0
 *     </tr>
 *     </tbody>
 *   </table>
 *
 * <p>
 * The differences between this format and the
 * standard UTF-8 format are the following:
 * <ul>
 * <li>The null byte {@code '\u005Cu0000'} is encoded in 2-byte format
 *     rather than 1-byte, so that the encoded strings never have
 *     embedded nulls.
 * <li>Only the 1-byte, 2-byte, and 3-byte formats are used.
 * <li><a href="../lang/Character.html#unicode">Supplementary characters</a>
 *     are represented in the form of surrogate pairs.
 * </ul>
 * @author  Frank Yellin
 * @see     java.io.DataInputStream
 * @see     java.io.DataOutput
 * @since   1.0
 */
public
interface DataInput {
    
Reads some bytes from an input stream and stores them into the buffer array b. The number of bytes read is equal to the length of b. 

This method blocks until one of the
following conditions occurs:

    

  • b.length bytes of input data are available, in which case a normal return is made. 
  • End of file is detected, in which case an EOFException is thrown. 
  • An I/O error occurs, in which case an IOException other than EOFException is thrown. 


 If b is null, a NullPointerException is thrown. If b.length is zero, then no bytes are read. Otherwise, the first byte read is stored into element b[0], the next one into b[1], and so on. If an exception is thrown from this method, then it may be that some but not all bytes of b have been updated with data from the input stream. 
Params:
  • b –   the buffer into which the data is read.
Throws:
/**
     * Reads some bytes from an input
     * stream and stores them into the buffer
     * array {@code b}. The number of bytes
     * read is equal
     * to the length of {@code b}.
     * <p>
     * This method blocks until one of the
     * following conditions occurs:
     * <ul>
     * <li>{@code b.length}
     * bytes of input data are available, in which
     * case a normal return is made.
     *
     * <li>End of
     * file is detected, in which case an {@code EOFException}
     * is thrown.
     *
     * <li>An I/O error occurs, in
     * which case an {@code IOException} other
     * than {@code EOFException} is thrown.
     * </ul>
     * <p>
     * If {@code b} is {@code null},
     * a {@code NullPointerException} is thrown.
     * If {@code b.length} is zero, then
     * no bytes are read. Otherwise, the first
     * byte read is stored into element {@code b[0]},
     * the next one into {@code b[1]}, and
     * so on.
     * If an exception is thrown from
     * this method, then it may be that some but
     * not all bytes of {@code b} have been
     * updated with data from the input stream.
     *
     * @param   b   the buffer into which the data is read.
     * @throws  NullPointerException if {@code b} is {@code null}.
     * @throws  EOFException  if this stream reaches the end before reading
     *          all the bytes.
     * @throws  IOException   if an I/O error occurs.
     */
    void readFully(byte b[]) throws IOException;

    
Reads len bytes from an input stream. 

This method
blocks until one of the following conditions
occurs:

    

  • len bytes of input data are available, in which case a normal return is made. 
  • End of file is detected, in which case an EOFException is thrown. 
  • An I/O error occurs, in which case an IOException other than EOFException is thrown. 


 If b is null, a NullPointerException is thrown. If off is negative, or len is negative, or off+len is greater than the length of the array b, then an IndexOutOfBoundsException is thrown. If len is zero, then no bytes are read. Otherwise, the first byte read is stored into element b[off], the next one into b[off+1], and so on. The number of bytes read is, at most, equal to len. 
Params:
  • b –    the buffer into which the data is read.
  • off –  an int specifying the offset in the data array b.
  • len –  an int specifying the number of bytes to read.
Throws:
/**
     *
     * Reads {@code len}
     * bytes from
     * an input stream.
     * <p>
     * This method
     * blocks until one of the following conditions
     * occurs:
     * <ul>
     * <li>{@code len} bytes
     * of input data are available, in which case
     * a normal return is made.
     *
     * <li>End of file
     * is detected, in which case an {@code EOFException}
     * is thrown.
     *
     * <li>An I/O error occurs, in
     * which case an {@code IOException} other
     * than {@code EOFException} is thrown.
     * </ul>
     * <p>
     * If {@code b} is {@code null},
     * a {@code NullPointerException} is thrown.
     * If {@code off} is negative, or {@code len}
     * is negative, or {@code off+len} is
     * greater than the length of the array {@code b},
     * then an {@code IndexOutOfBoundsException}
     * is thrown.
     * If {@code len} is zero,
     * then no bytes are read. Otherwise, the first
     * byte read is stored into element {@code b[off]},
     * the next one into {@code b[off+1]},
     * and so on. The number of bytes read is,
     * at most, equal to {@code len}.
     *
     * @param   b    the buffer into which the data is read.
     * @param   off  an int specifying the offset in the data array {@code b}.
     * @param   len  an int specifying the number of bytes to read.
     * @throws  NullPointerException if {@code b} is {@code null}.
     * @throws  IndexOutOfBoundsException if {@code off} is negative,
     *          {@code len} is negative, or {@code len} is greater than
     *          {@code b.length - off}.
     * @throws  EOFException  if this stream reaches the end before reading
     *          all the bytes.
     * @throws  IOException   if an I/O error occurs.
     */
    void readFully(byte b[], int off, int len) throws IOException;

    
Makes an attempt to skip over n bytes of data from the input stream, discarding the skipped bytes. However, it may skip over some smaller number of bytes, possibly zero. This may result from any of a number of conditions; reaching end of file before n bytes have been skipped is only one possibility. This method never throws an EOFException. The actual number of bytes skipped is returned. 
Params:
  • n –   the number of bytes to be skipped.
Throws:
Returns:    the number of bytes actually skipped.
/**
     * Makes an attempt to skip over
     * {@code n} bytes
     * of data from the input
     * stream, discarding the skipped bytes. However,
     * it may skip
     * over some smaller number of
     * bytes, possibly zero. This may result from
     * any of a
     * number of conditions; reaching
     * end of file before {@code n} bytes
     * have been skipped is
     * only one possibility.
     * This method never throws an {@code EOFException}.
     * The actual
     * number of bytes skipped is returned.
     *
     * @param      n   the number of bytes to be skipped.
     * @return     the number of bytes actually skipped.
     * @exception  IOException   if an I/O error occurs.
     */
    int skipBytes(int n) throws IOException;

    
Reads one input byte and returns true if that byte is nonzero, false if that byte is zero. This method is suitable for reading the byte written by the writeBoolean method of interface DataOutput. 
Throws:
  • EOFException –  if this stream reaches the end before reading
              all the bytes.
  • IOException –   if an I/O error occurs.
Returns: the boolean value read.
/**
     * Reads one input byte and returns
     * {@code true} if that byte is nonzero,
     * {@code false} if that byte is zero.
     * This method is suitable for reading
     * the byte written by the {@code writeBoolean}
     * method of interface {@code DataOutput}.
     *
     * @return     the {@code boolean} value read.
     * @exception  EOFException  if this stream reaches the end before reading
     *               all the bytes.
     * @exception  IOException   if an I/O error occurs.
     */
    boolean readBoolean() throws IOException;

    
Reads and returns one input byte. The byte is treated as a signed value in the range -128 through 127, inclusive. This method is suitable for reading the byte written by the writeByte method of interface DataOutput. 
Throws:
  • EOFException –  if this stream reaches the end before reading
              all the bytes.
  • IOException –   if an I/O error occurs.
Returns:    the 8-bit value read.
/**
     * Reads and returns one input byte.
     * The byte is treated as a signed value in
     * the range {@code -128} through {@code 127},
     * inclusive.
     * This method is suitable for
     * reading the byte written by the {@code writeByte}
     * method of interface {@code DataOutput}.
     *
     * @return     the 8-bit value read.
     * @exception  EOFException  if this stream reaches the end before reading
     *               all the bytes.
     * @exception  IOException   if an I/O error occurs.
     */
    byte readByte() throws IOException;

    
Reads one input byte, zero-extends it to type int, and returns the result, which is therefore in the range 0 through 255. This method is suitable for reading the byte written by the writeByte method of interface DataOutput if the argument to writeByte was intended to be a value in the range 0 through 255. 
Throws:
  • EOFException –  if this stream reaches the end before reading
              all the bytes.
  • IOException –   if an I/O error occurs.
Returns:    the unsigned 8-bit value read.
/**
     * Reads one input byte, zero-extends
     * it to type {@code int}, and returns
     * the result, which is therefore in the range
     * {@code 0}
     * through {@code 255}.
     * This method is suitable for reading
     * the byte written by the {@code writeByte}
     * method of interface {@code DataOutput}
     * if the argument to {@code writeByte}
     * was intended to be a value in the range
     * {@code 0} through {@code 255}.
     *
     * @return     the unsigned 8-bit value read.
     * @exception  EOFException  if this stream reaches the end before reading
     *               all the bytes.
     * @exception  IOException   if an I/O error occurs.
     */
    int readUnsignedByte() throws IOException;

    
Reads two input bytes and returns a short value. Let a be the first byte read and b be the second byte. The value returned is: 
(short)((a << 8) | (b & 0xff))

 This method is suitable for reading the bytes written by the writeShort method of interface DataOutput. 
Throws:
  • EOFException –  if this stream reaches the end before reading
              all the bytes.
  • IOException –   if an I/O error occurs.
Returns:    the 16-bit value read.
/**
     * Reads two input bytes and returns
     * a {@code short} value. Let {@code a}
     * be the first byte read and {@code b}
     * be the second byte. The value
     * returned
     * is:
     * <pre>{@code (short)((a << 8) | (b & 0xff))
     * }</pre>
     * This method
     * is suitable for reading the bytes written
     * by the {@code writeShort} method of
     * interface {@code DataOutput}.
     *
     * @return     the 16-bit value read.
     * @exception  EOFException  if this stream reaches the end before reading
     *               all the bytes.
     * @exception  IOException   if an I/O error occurs.
     */
    short readShort() throws IOException;

    
Reads two input bytes and returns an int value in the range 0 through 65535. Let a be the first byte read and b be the second byte. The value returned is: 
(((a & 0xff) << 8) | (b & 0xff))

 This method is suitable for reading the bytes written by the writeShort method of interface DataOutput if the argument to writeShort was intended to be a value in the range 0 through 65535. 
Throws:
  • EOFException –  if this stream reaches the end before reading
              all the bytes.
  • IOException –   if an I/O error occurs.
Returns:    the unsigned 16-bit value read.
/**
     * Reads two input bytes and returns
     * an {@code int} value in the range {@code 0}
     * through {@code 65535}. Let {@code a}
     * be the first byte read and
     * {@code b}
     * be the second byte. The value returned is:
     * <pre>{@code (((a & 0xff) << 8) | (b & 0xff))
     * }</pre>
     * This method is suitable for reading the bytes
     * written by the {@code writeShort} method
     * of interface {@code DataOutput}  if
     * the argument to {@code writeShort}
     * was intended to be a value in the range
     * {@code 0} through {@code 65535}.
     *
     * @return     the unsigned 16-bit value read.
     * @exception  EOFException  if this stream reaches the end before reading
     *               all the bytes.
     * @exception  IOException   if an I/O error occurs.
     */
    int readUnsignedShort() throws IOException;

    
Reads two input bytes and returns a char value. Let a be the first byte read and b be the second byte. The value returned is: 
(char)((a << 8) | (b & 0xff))

 This method is suitable for reading bytes written by the writeChar method of interface DataOutput. 
Throws:
  • EOFException –  if this stream reaches the end before reading
              all the bytes.
  • IOException –   if an I/O error occurs.
Returns: the char value read.
/**
     * Reads two input bytes and returns a {@code char} value.
     * Let {@code a}
     * be the first byte read and {@code b}
     * be the second byte. The value
     * returned is:
     * <pre>{@code (char)((a << 8) | (b & 0xff))
     * }</pre>
     * This method
     * is suitable for reading bytes written by
     * the {@code writeChar} method of interface
     * {@code DataOutput}.
     *
     * @return     the {@code char} value read.
     * @exception  EOFException  if this stream reaches the end before reading
     *               all the bytes.
     * @exception  IOException   if an I/O error occurs.
     */
    char readChar() throws IOException;

    
Reads four input bytes and returns an int value. Let a-d be the first through fourth bytes read. The value returned is: 

(((a & 0xff) << 24) | ((b & 0xff) << 16) |
 ((c & 0xff) <<  8) | (d & 0xff))

 This method is suitable for reading bytes written by the writeInt method of interface DataOutput. 
Throws:
  • EOFException –  if this stream reaches the end before reading
              all the bytes.
  • IOException –   if an I/O error occurs.
Returns: the int value read.
/**
     * Reads four input bytes and returns an
     * {@code int} value. Let {@code a-d}
     * be the first through fourth bytes read. The value returned is:
     * <pre>{@code
     * (((a & 0xff) << 24) | ((b & 0xff) << 16) |
     *  ((c & 0xff) <<  8) | (d & 0xff))
     * }</pre>
     * This method is suitable
     * for reading bytes written by the {@code writeInt}
     * method of interface {@code DataOutput}.
     *
     * @return     the {@code int} value read.
     * @exception  EOFException  if this stream reaches the end before reading
     *               all the bytes.
     * @exception  IOException   if an I/O error occurs.
     */
    int readInt() throws IOException;

    
Reads eight input bytes and returns a long value. Let a-h be the first through eighth bytes read. The value returned is: 

(((long)(a & 0xff) << 56) |
 ((long)(b & 0xff) << 48) |
 ((long)(c & 0xff) << 40) |
 ((long)(d & 0xff) << 32) |
 ((long)(e & 0xff) << 24) |
 ((long)(f & 0xff) << 16) |
 ((long)(g & 0xff) <<  8) |
 ((long)(h & 0xff)))



 This method is suitable for reading bytes written by the writeLong method of interface DataOutput. 
Throws:
  • EOFException –  if this stream reaches the end before reading
              all the bytes.
  • IOException –   if an I/O error occurs.
Returns: the long value read.
/**
     * Reads eight input bytes and returns
     * a {@code long} value. Let {@code a-h}
     * be the first through eighth bytes read.
     * The value returned is:
     * <pre>{@code
     * (((long)(a & 0xff) << 56) |
     *  ((long)(b & 0xff) << 48) |
     *  ((long)(c & 0xff) << 40) |
     *  ((long)(d & 0xff) << 32) |
     *  ((long)(e & 0xff) << 24) |
     *  ((long)(f & 0xff) << 16) |
     *  ((long)(g & 0xff) <<  8) |
     *  ((long)(h & 0xff)))
     * }</pre>
     * <p>
     * This method is suitable
     * for reading bytes written by the {@code writeLong}
     * method of interface {@code DataOutput}.
     *
     * @return     the {@code long} value read.
     * @exception  EOFException  if this stream reaches the end before reading
     *               all the bytes.
     * @exception  IOException   if an I/O error occurs.
     */
    long readLong() throws IOException;

    
Reads four input bytes and returns a float value. It does this by first constructing an int value in exactly the manner of the readInt method, then converting this int value to a float in exactly the manner of the method Float.intBitsToFloat. This method is suitable for reading bytes written by the writeFloat method of interface DataOutput. 
Throws:
  • EOFException –  if this stream reaches the end before reading
              all the bytes.
  • IOException –   if an I/O error occurs.
Returns: the float value read.
/**
     * Reads four input bytes and returns
     * a {@code float} value. It does this
     * by first constructing an {@code int}
     * value in exactly the manner
     * of the {@code readInt}
     * method, then converting this {@code int}
     * value to a {@code float} in
     * exactly the manner of the method {@code Float.intBitsToFloat}.
     * This method is suitable for reading
     * bytes written by the {@code writeFloat}
     * method of interface {@code DataOutput}.
     *
     * @return     the {@code float} value read.
     * @exception  EOFException  if this stream reaches the end before reading
     *               all the bytes.
     * @exception  IOException   if an I/O error occurs.
     */
    float readFloat() throws IOException;

    
Reads eight input bytes and returns a double value. It does this by first constructing a long value in exactly the manner of the readLong method, then converting this long value to a double in exactly the manner of the method Double.longBitsToDouble. This method is suitable for reading bytes written by the writeDouble method of interface DataOutput. 
Throws:
  • EOFException –  if this stream reaches the end before reading
              all the bytes.
  • IOException –   if an I/O error occurs.
Returns: the double value read.
/**
     * Reads eight input bytes and returns
     * a {@code double} value. It does this
     * by first constructing a {@code long}
     * value in exactly the manner
     * of the {@code readLong}
     * method, then converting this {@code long}
     * value to a {@code double} in exactly
     * the manner of the method {@code Double.longBitsToDouble}.
     * This method is suitable for reading
     * bytes written by the {@code writeDouble}
     * method of interface {@code DataOutput}.
     *
     * @return     the {@code double} value read.
     * @exception  EOFException  if this stream reaches the end before reading
     *               all the bytes.
     * @exception  IOException   if an I/O error occurs.
     */
    double readDouble() throws IOException;

    
Reads the next line of text from the input stream. It reads successive bytes, converting each byte separately into a character, until it encounters a line terminator or end of file; the characters read are then returned as a String. Note that because this method processes bytes, it does not support input of the full Unicode character set. 
 If end of file is encountered before even one byte can be read, then null is returned. Otherwise, each byte that is read is converted to type char by zero-extension. If the character '\n' is encountered, it is discarded and reading ceases. If the character '\r' is encountered, it is discarded and, if the following byte converts to the character '\n', then that is discarded also; reading then ceases. If end of file is encountered before either of the characters '\n' and '\r' is encountered, reading ceases. Once reading has ceased, a String is returned that contains all the characters read and not discarded, taken in order. Note that every character in this string will have a value less than \u005Cu0100, that is, (char)256. 
Throws:
Returns:the next line of text from the input stream, or null if the end of file is encountered before a byte can be read.
/**
     * Reads the next line of text from the input stream.
     * It reads successive bytes, converting
     * each byte separately into a character,
     * until it encounters a line terminator or
     * end of
     * file; the characters read are then
     * returned as a {@code String}. Note
     * that because this
     * method processes bytes,
     * it does not support input of the full Unicode
     * character set.
     * <p>
     * If end of file is encountered
     * before even one byte can be read, then {@code null}
     * is returned. Otherwise, each byte that is
     * read is converted to type {@code char}
     * by zero-extension. If the character {@code '\n'}
     * is encountered, it is discarded and reading
     * ceases. If the character {@code '\r'}
     * is encountered, it is discarded and, if
     * the following byte converts &#32;to the
     * character {@code '\n'}, then that is
     * discarded also; reading then ceases. If
     * end of file is encountered before either
     * of the characters {@code '\n'} and
     * {@code '\r'} is encountered, reading
     * ceases. Once reading has ceased, a {@code String}
     * is returned that contains all the characters
     * read and not discarded, taken in order.
     * Note that every character in this string
     * will have a value less than {@code \u005Cu0100},
     * that is, {@code (char)256}.
     *
     * @return the next line of text from the input stream,
     *         or {@code null} if the end of file is
     *         encountered before a byte can be read.
     * @exception  IOException  if an I/O error occurs.
     */
    String readLine() throws IOException;

    
Reads in a string that has been encoded using a
modified UTF-8 format. The general contract of readUTF is that it reads a representation of a Unicode character string encoded in modified UTF-8 format; this string of characters is then returned as a String. 
 First, two bytes are read and used to construct an unsigned 16-bit integer in exactly the manner of the readUnsignedShort method . This integer value is called the UTF length and specifies the number
of additional bytes to be read. These bytes
are then converted to characters by considering
them in groups. The length of each group
is computed from the value of the first
byte of the group. The byte following a
group, if any, is the first byte of the
next group.

 If the first byte of a group matches the bit pattern 0xxxxxxx (where x means "may be 0 or 1"), then the group consists of just that byte. The byte is zero-extended to form a character. 
 If the first byte of a group matches the bit pattern 110xxxxx, then the group consists of that byte a and a second byte b. If there is no byte b (because byte a was the last of the bytes to be read), or if byte b does not match the bit pattern 10xxxxxx, then a UTFDataFormatException is thrown. Otherwise, the group is converted to the character: 
(char)(((a & 0x1F) << 6) | (b & 0x3F))

 If the first byte of a group matches the bit pattern 1110xxxx, then the group consists of that byte a and two more bytes b and c. If there is no byte c (because byte a was one of the last two of the bytes to be read), or either byte b or byte c does not match the bit pattern 10xxxxxx, then a UTFDataFormatException is thrown. Otherwise, the group is converted to the character: 

(char)(((a & 0x0F) << 12) | ((b & 0x3F) << 6) | (c & 0x3F))

 If the first byte of a group matches the pattern 1111xxxx or the pattern 10xxxxxx, then a UTFDataFormatException is thrown. 
 If end of file is encountered at any time during this entire process, then an EOFException is thrown. 
 After every group has been converted to a character by this process, the characters are gathered, in the same order in which their corresponding groups were read from the input stream, to form a String, which is returned. 
 The writeUTF method of interface DataOutput may be used to write data that is suitable for reading by this method. 
Throws:
Returns:    a Unicode string.
/**
     * Reads in a string that has been encoded using a
     * <a href="#modified-utf-8">modified UTF-8</a>
     * format.
     * The general contract of {@code readUTF}
     * is that it reads a representation of a Unicode
     * character string encoded in modified
     * UTF-8 format; this string of characters
     * is then returned as a {@code String}.
     * <p>
     * First, two bytes are read and used to
     * construct an unsigned 16-bit integer in
     * exactly the manner of the {@code readUnsignedShort}
     * method . This integer value is called the
     * <i>UTF length</i> and specifies the number
     * of additional bytes to be read. These bytes
     * are then converted to characters by considering
     * them in groups. The length of each group
     * is computed from the value of the first
     * byte of the group. The byte following a
     * group, if any, is the first byte of the
     * next group.
     * <p>
     * If the first byte of a group
     * matches the bit pattern {@code 0xxxxxxx}
     * (where {@code x} means "may be {@code 0}
     * or {@code 1}"), then the group consists
     * of just that byte. The byte is zero-extended
     * to form a character.
     * <p>
     * If the first byte
     * of a group matches the bit pattern {@code 110xxxxx},
     * then the group consists of that byte {@code a}
     * and a second byte {@code b}. If there
     * is no byte {@code b} (because byte
     * {@code a} was the last of the bytes
     * to be read), or if byte {@code b} does
     * not match the bit pattern {@code 10xxxxxx},
     * then a {@code UTFDataFormatException}
     * is thrown. Otherwise, the group is converted
     * to the character:
     * <pre>{@code (char)(((a & 0x1F) << 6) | (b & 0x3F))
     * }</pre>
     * If the first byte of a group
     * matches the bit pattern {@code 1110xxxx},
     * then the group consists of that byte {@code a}
     * and two more bytes {@code b} and {@code c}.
     * If there is no byte {@code c} (because
     * byte {@code a} was one of the last
     * two of the bytes to be read), or either
     * byte {@code b} or byte {@code c}
     * does not match the bit pattern {@code 10xxxxxx},
     * then a {@code UTFDataFormatException}
     * is thrown. Otherwise, the group is converted
     * to the character:
     * <pre>{@code
     * (char)(((a & 0x0F) << 12) | ((b & 0x3F) << 6) | (c & 0x3F))
     * }</pre>
     * If the first byte of a group matches the
     * pattern {@code 1111xxxx} or the pattern
     * {@code 10xxxxxx}, then a {@code UTFDataFormatException}
     * is thrown.
     * <p>
     * If end of file is encountered
     * at any time during this entire process,
     * then an {@code EOFException} is thrown.
     * <p>
     * After every group has been converted to
     * a character by this process, the characters
     * are gathered, in the same order in which
     * their corresponding groups were read from
     * the input stream, to form a {@code String},
     * which is returned.
     * <p>
     * The {@code writeUTF}
     * method of interface {@code DataOutput}
     * may be used to write data that is suitable
     * for reading by this method.
     * @return     a Unicode string.
     * @exception  EOFException            if this stream reaches the end
     *               before reading all the bytes.
     * @exception  IOException             if an I/O error occurs.
     * @exception  UTFDataFormatException  if the bytes do not represent a
     *               valid modified UTF-8 encoding of a string.
     */
    String readUTF() throws IOException;
}