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 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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package java.io;

/**
 * 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.
 *
 * <h3><a name="modified-utf-8">Modified UTF-8</a></h3>
 * <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>).
 * Note that in the following table, the most significant bit appears in the
 * far left-hand column.
 *
 * <blockquote>
 * <table border="1" cellspacing="0" cellpadding="8"
 * summary="Bit values and bytes">
 * <tr>
 * <th colspan="9"><span style="font-weight:normal">
 * All characters in the range {@code '\u005Cu0001'} to
 * {@code '\u005Cu007F'} are represented by a single byte:</span></th>
 * </tr>
 * <tr>
 * <td></td>
 * <th colspan="8" id="bit_a">Bit Values</th>
 * </tr>
 * <tr>
 * <th id="byte1_a">Byte 1</th>
 * <td><center>0</center>
 * <td colspan="7"><center>bits 6-0</center>
 * </tr>
 * <tr>
 * <th colspan="9"><span style="font-weight:normal">
 * The null character {@code '\u005Cu0000'} and characters
 * in the range {@code '\u005Cu0080'} to {@code '\u005Cu07FF'} are
 * represented by a pair of bytes:</span></th>
 * </tr>
 * <tr>
 * <td></td>
 * <th colspan="8" id="bit_b">Bit Values</th>
 * </tr>
 * <tr>
 * <th id="byte1_b">Byte 1</th>
 * <td><center>1</center>
 * <td><center>1</center>
 * <td><center>0</center>
 * <td colspan="5"><center>bits 10-6</center>
 * </tr>
 * <tr>
 * <th id="byte2_a">Byte 2</th>
 * <td><center>1</center>
 * <td><center>0</center>
 * <td colspan="6"><center>bits 5-0</center>
 * </tr>
 * <tr>
 * <th colspan="9"><span style="font-weight:normal">
 * {@code char} values in the range {@code '\u005Cu0800'}
 * to {@code '\u005CuFFFF'} are represented by three bytes:</span></th>
 * </tr>
 * <tr>
 * <td></td>
 * <th colspan="8"id="bit_c">Bit Values</th>
 * </tr>
 * <tr>
 * <th id="byte1_c">Byte 1</th>
 * <td><center>1</center>
 * <td><center>1</center>
 * <td><center>1</center>
 * <td><center>0</center>
 * <td colspan="4"><center>bits 15-12</center>
 * </tr>
 * <tr>
 * <th id="byte2_b">Byte 2</th>
 * <td><center>1</center>
 * <td><center>0</center>
 * <td colspan="6"><center>bits 11-6</center>
 * </tr>
 * <tr>
 * <th id="byte3">Byte 3</th>
 * <td><center>1</center>
 * <td><center>0</center>
 * <td colspan="6"><center>bits 5-0</center>
 * </tr>
 * </table>
 * </blockquote>
 * <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 JDK1.0
 */
public
interface DataInput {
 /**
 * 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.
 * @exception EOFException if this stream reaches the end before reading
 * all the bytes.
 * @exception IOException if an I/O error occurs.
 */
 void readFully(byte b[]) throws IOException;

 /**
 *
 * 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 into the data.
 * @param len an int specifying the number of bytes to read.
 * @exception EOFException if this stream reaches the end before reading
 * all the bytes.
 * @exception IOException if an I/O error occurs.
 */
 void readFully(byte b[], int off, int len) throws IOException;

 /**
 * 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
 * {@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 {@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 {@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 {@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 {@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 {@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
 * {@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 {@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 {@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 {@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 {@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
 * <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;
}