Back to index...

	/*
	* 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 {@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 {@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 {@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
	* {@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.
	* @throws 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.
	* @throws EOFException if this stream reaches the end before reading
	* all the bytes.
	* @throws 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.
	* @throws EOFException if this stream reaches the end before reading
	* all the bytes.
	* @throws 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.
	* @throws EOFException if this stream reaches the end before reading
	* all the bytes.
	* @throws 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.
	* @throws EOFException if this stream reaches the end before reading
	* all the bytes.
	* @throws 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.
	* @throws EOFException if this stream reaches the end before reading
	* all the bytes.
	* @throws 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.
	* @throws EOFException if this stream reaches the end before reading
	* all the bytes.
	* @throws 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.
	* @throws EOFException if this stream reaches the end before reading
	* all the bytes.
	* @throws 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.
	* @throws EOFException if this stream reaches the end before reading
	* all the bytes.
	* @throws 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.
	* @throws EOFException if this stream reaches the end before reading
	* all the bytes.
	* @throws 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.
	* @throws EOFException if this stream reaches the end before reading
	* all the bytes.
	* @throws 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 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.
	* @throws 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.
	* @throws EOFException if this stream reaches the end
	* before reading all the bytes.
	* @throws IOException if an I/O error occurs.
	* @throws UTFDataFormatException if the bytes do not represent a
	* valid modified UTF-8 encoding of a string.
	*/
	String readUTF() throws IOException;
	}

Back to index...