/*
* @(#)DataInput.java 1.23 04/06/03
*
* Copyright 2004 Sun Microsystems, Inc. All rights reserved.
* SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*/
package java.io;
/**
* The <code>DataInput</code> 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</code>
* 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</code>
* (which is a kind of <code>IOException</code>)
* is thrown. If any byte cannot be read for
* any reason other than end of file, an <code>IOException</code>
* other than <code>EOFException</code> is
* thrown. In particular, an <code>IOException</code>
* may be thrown if the input stream has been
* closed.
*
* <h4><a name="modified-utf-8">Modified UTF-8</a></h4>
* <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 tables, the most significant bit appears in the
* far left-hand column.
* <p>
* All characters in the range <code>'\u0001'</code> to
* <code>'\u007F'</code> are represented by a single byte:
*
* <blockquote>
* <table border="1" cellspacing="0" cellpadding="8" width="50%"
* summary="Bit values and bytes">
* <tr>
* <td></td>
* <th id="bit">Bit Values</th>
* </tr>
* <tr>
* <th id="byte1">Byte 1</th>
* <td>
* <table border="1" cellspacing="0" width="100%">
* <tr>
* <td width="12%"><center>0</center>
* <td colspan="7"><center>bits 6-0</center>
* </tr>
* </table>
* </td>
* </tr>
* </table>
* </blockquote>
*
* <p>
* The null character <code>'\u0000'</code> and characters in the
* range <code>'\u0080'</code> to <code>'\u07FF'</code> are
* represented by a pair of bytes:
*
* <blockquote>
* <table border="1" cellspacing="0" cellpadding="8" width="50%"
* summary="Bit values and bytes">
* <tr>
* <td></td>
* <th id="bit">Bit Values</th>
* </tr>
* <tr>
* <th id="byte1">Byte 1</th>
* <td>
* <table border="1" cellspacing="0" width="100%">
* <tr>
* <td width="12%"><center>1</center>
* <td width="13%"><center>1</center>
* <td width="12%"><center>0</center>
* <td colspan="5"><center>bits 10-6</center>
* </tr>
* </table>
* </td>
* </tr>
* <tr>
* <th id="byte2">Byte 2</th>
* <td>
* <table border="1" cellspacing="0" width="100%">
* <tr>
* <td width="12%"><center>1</center>
* <td width="13%"><center>0</center>
* <td colspan="6"><center>bits 5-0</center>
* </tr>
* </table>
* </td>
* </tr>
* </table>
* </blockquote>
*
* <br>
* <code>char</code> values in the range <code>'\u0800'</code> to
* <code>'\uFFFF'</code> are represented by three bytes:
*
* <blockquote>
* <table border="1" cellspacing="0" cellpadding="8" width="50%"
* summary="Bit values and bytes">
* <tr>
* <td></td>
* <th id="bit">Bit Values</th>
* </tr>
* <tr>
* <th id="byte1">Byte 1</th>
* <td>
* <table border="1" cellspacing="0" width="100%">
* <tr>
* <td width="12%"><center>1</center>
* <td width="13%"><center>1</center>
* <td width="12%"><center>1</center>
* <td width="13%"><center>0</center>
* <td colspan="4"><center>bits 15-12</center>
* </tr>
* </table>
* </td>
* </tr>
* <tr>
* <th id="byte2">Byte 2</th>
* <td>
* <table border="1" cellspacing="0" width="100%">
* <tr>
* <td width="12%"><center>1</center>
* <td width="13%"><center>0</center>
* <td colspan="6"><center>bits 11-6</center>
* </tr>
* </table>
* </td>
* </tr>
* <tr>
* <th id="byte3">Byte 3</th>
* <td>
* <table border="1" cellspacing="0" width="100%">
* <tr>
* <td width="12%"><center>1</center>
* <td width="13%"><center>0</center>
* <td colspan="6"><center>bits 5-0</center>
* </tr>
* </table>
* </td>
* </tr>
* </table>
* </blockquote>
*
* <p>
* The differences between this format and the
* standard UTF-8 format are the following:
* <ul>
* <li>The null byte <code>'\u0000'</code> 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
* @version 1.23, 06/03/04
* @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</code>. The number of bytes
* read is equal
* to the length of <code>b</code>.
* <p>
* This method blocks until one of the
* following conditions occurs:<p>
* <ul>
* <li><code>b.length</code>
* 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</code>
* is thrown.
*
* <li>An I/O error occurs, in
* which case an <code>IOException</code> other
* than <code>EOFException</code> is thrown.
* </ul>
* <p>
* If <code>b</code> is <code>null</code>,
* a <code>NullPointerException</code> is thrown.
* If <code>b.length</code> is zero, then
* no bytes are read. Otherwise, the first
* byte read is stored into element <code>b[0]</code>,
* the next one into <code>b[1]</code>, and
* so on.
* If an exception is thrown from
* this method, then it may be that some but
* not all bytes of <code>b</code> 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</code>
* bytes from
* an input stream.
* <p>
* This method
* blocks until one of the following conditions
* occurs:<p>
* <ul>
* <li><code>len</code> 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</code>
* is thrown.
*
* <li>An I/O error occurs, in
* which case an <code>IOException</code> other
* than <code>EOFException</code> is thrown.
* </ul>
* <p>
* If <code>b</code> is <code>null</code>,
* a <code>NullPointerException</code> is thrown.
* If <code>off</code> is negative, or <code>len</code>
* is negative, or <code>off+len</code> is
* greater than the length of the array <code>b</code>,
* then an <code>IndexOutOfBoundsException</code>
* is thrown.
* If <code>len</code> is zero,
* then no bytes are read. Otherwise, the first
* byte read is stored into element <code>b[off]</code>,
* the next one into <code>b[off+1]</code>,
* and so on. The number of bytes read is,
* at most, equal to <code>len</code>.
*
* @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</code> 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</code> bytes
* have been skipped is
* only one possibility.
* This method never throws an <code>EOFException</code>.
* 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</code> if that byte is nonzero,
* <code>false</code> if that byte is zero.
* This method is suitable for reading
* the byte written by the <code>writeBoolean</code>
* method of interface <code>DataOutput</code>.
*
* @return the <code>boolean</code> 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</code> through <code>127</code>,
* inclusive.
* This method is suitable for
* reading the byte written by the <code>writeByte</code>
* method of interface <code>DataOutput</code>.
*
* @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</code>, and returns
* the result, which is therefore in the range
* <code>0</code>
* through <code>255</code>.
* This method is suitable for reading
* the byte written by the <code>writeByte</code>
* method of interface <code>DataOutput</code>
* if the argument to <code>writeByte</code>
* was intended to be a value in the range
* <code>0</code> through <code>255</code>.
*
* @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</code> value. Let <code>a</code>
* be the first byte read and <code>b</code>
* be the second byte. The value
* returned
* is:
* <p><pre><code>(short)((a << 8) | (b & 0xff))
* </code></pre>
* This method
* is suitable for reading the bytes written
* by the <code>writeShort</code> method of
* interface <code>DataOutput</code>.
*
* @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</code> value in the range <code>0</code>
* through <code>65535</code>. Let <code>a</code>
* be the first byte read and
* <code>b</code>
* be the second byte. The value returned is:
* <p><pre><code>(((a & 0xff) << 8) | (b & 0xff))
* </code></pre>
* This method is suitable for reading the bytes
* written by the <code>writeShort</code> method
* of interface <code>DataOutput</code> if
* the argument to <code>writeShort</code>
* was intended to be a value in the range
* <code>0</code> through <code>65535</code>.
*
* @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 an input <code>char</code> and returns the <code>char</code> value.
* A Unicode <code>char</code> is made up of two bytes.
* Let <code>a</code>
* be the first byte read and <code>b</code>
* be the second byte. The value
* returned is:
* <p><pre><code>(char)((a << 8) | (b & 0xff))
* </code></pre>
* This method
* is suitable for reading bytes written by
* the <code>writeChar</code> method of interface
* <code>DataOutput</code>.
*
* @return the Unicode <code>char</code> 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</code> value. Let <code>a</code>
* be the first byte read, <code>b</code> be
* the second byte, <code>c</code> be the third
* byte,
* and <code>d</code> be the fourth
* byte. The value returned is:
* <p><pre>
* <code>
* (((a & 0xff) << 24) | ((b & 0xff) << 16) |
* ((c & 0xff) << 8) | (d & 0xff))
* </code></pre>
* This method is suitable
* for reading bytes written by the <code>writeInt</code>
* method of interface <code>DataOutput</code>.
*
* @return the <code>int</code> 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</code> value. Let <code>a</code>
* be the first byte read, <code>b</code> be
* the second byte, <code>c</code> be the third
* byte, <code>d</code>
* be the fourth byte,
* <code>e</code> be the fifth byte, <code>f</code>
* be the sixth byte, <code>g</code> be the
* seventh byte,
* and <code>h</code> be the
* eighth byte. The value returned is:
* <p><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)))
* </code></pre>
* <p>
* This method is suitable
* for reading bytes written by the <code>writeLong</code>
* method of interface <code>DataOutput</code>.
*
* @return the <code>long</code> 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</code> value. It does this
* by first constructing an <code>int</code>
* value in exactly the manner
* of the <code>readInt</code>
* method, then converting this <code>int</code>
* value to a <code>float</code> in
* exactly the manner of the method <code>Float.intBitsToFloat</code>.
* This method is suitable for reading
* bytes written by the <code>writeFloat</code>
* method of interface <code>DataOutput</code>.
*
* @return the <code>float</code> 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</code> value. It does this
* by first constructing a <code>long</code>
* value in exactly the manner
* of the <code>readlong</code>
* method, then converting this <code>long</code>
* value to a <code>double</code> in exactly
* the manner of the method <code>Double.longBitsToDouble</code>.
* This method is suitable for reading
* bytes written by the <code>writeDouble</code>
* method of interface <code>DataOutput</code>.
*
* @return the <code>double</code> 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</code>. 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</code>
* is returned. Otherwise, each byte that is
* read is converted to type <code>char</code>
* by zero-extension. If the character <code>'\n'</code>
* is encountered, it is discarded and reading
* ceases. If the character <code>'\r'</code>
* is encountered, it is discarded and, if
* the following byte converts to the
* character <code>'\n'</code>, then that is
* discarded also; reading then ceases. If
* end of file is encountered before either
* of the characters <code>'\n'</code> and
* <code>'\r'</code> is encountered, reading
* ceases. Once reading has ceased, a <code>String</code>
* 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>\u0100</code>,
* that is, <code>(char)256</code>.
*
* @return the next line of text from the input stream,
* or <CODE>null</CODE> 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</code>
* 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</code>.
* <p>
* First, two bytes are read and used to
* construct an unsigned 16-bit integer in
* exactly the manner of the <code>readUnsignedShort</code>
* 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</code>
* (where <code>x</code> means "may be <code>0</code>
* or <code>1</code>"), 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</code>,
* then the group consists of that byte <code>a</code>
* and a second byte <code>b</code>. If there
* is no byte <code>b</code> (because byte
* <code>a</code> was the last of the bytes
* to be read), or if byte <code>b</code> does
* not match the bit pattern <code>10xxxxxx</code>,
* then a <code>UTFDataFormatException</code>
* is thrown. Otherwise, the group is converted
* to the character:<p>
* <pre><code>(char)(((a& 0x1F) << 6) | (b & 0x3F))
* </code></pre>
* If the first byte of a group
* matches the bit pattern <code>1110xxxx</code>,
* then the group consists of that byte <code>a</code>
* and two more bytes <code>b</code> and <code>c</code>.
* If there is no byte <code>c</code> (because
* byte <code>a</code> was one of the last
* two of the bytes to be read), or either
* byte <code>b</code> or byte <code>c</code>
* does not match the bit pattern <code>10xxxxxx</code>,
* then a <code>UTFDataFormatException</code>
* is thrown. Otherwise, the group is converted
* to the character:<p>
* <pre><code>
* (char)(((a & 0x0F) << 12) | ((b & 0x3F) << 6) | (c & 0x3F))
* </code></pre>
* If the first byte of a group matches the
* pattern <code>1111xxxx</code> or the pattern
* <code>10xxxxxx</code>, then a <code>UTFDataFormatException</code>
* is thrown.
* <p>
* If end of file is encountered
* at any time during this entire process,
* then an <code>EOFException</code> 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</code>,
* which is returned.
* <p>
* The <code>writeUTF</code>
* method of interface <code>DataOutput</code>
* 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;
}
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