-
DataInput
-
readFully(byte[]): void
-
readFully(byte[], int, int): void
-
skipBytes(int): int
-
readBoolean(): boolean
-
readByte(): byte
-
readUnsignedByte(): int
-
readShort(): short
-
readUnsignedShort(): int
-
readChar(): char
-
readInt(): int
-
readLong(): long
-
readFloat(): float
-
readDouble(): double
-
readLine(): String
-
readUTF(): String
-
/*
* Copyright (c) 1995, 2006, 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).
Note that in the following tables, the most significant bit appears in the
far left-hand column.
All characters in the range '\u0001' to
'\u007F' are represented by a single byte:
Bit Values
Byte 1
0
bits 6-0
The null character '\u0000' and characters in the
range '\u0080' to '\u07FF' are
represented by a pair of bytes:
Bit Values
Byte 1
1
1
0
bits 10-6
Byte 2
1
0
bits 5-0
char values in the range '\u0800' to
'\uFFFF' are represented by three bytes:
Bit Values
Byte 1
1
1
1
0
bits 15-12
Byte 2
1
0
bits 11-6
Byte 3
1
0
bits 5-0
The differences between this format and the
standard UTF-8 format are the following:
- The null byte
'\u0000' 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: JDK1.0
/**
* 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
* @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 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: - EOFException – if this stream reaches the end before reading
all the bytes.
- IOException – if an I/O error occurs.
/**
* 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 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 into the data.
- len – an int specifying the number of bytes to read.
Throws: - EOFException – if this stream reaches the end before reading
all the bytes.
- IOException – if an I/O error occurs.
/**
*
* 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
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: - IOException – if an I/O error occurs.
Returns: the number of bytes actually skipped.
/**
* 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
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</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 -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</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 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</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 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</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 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</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 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</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>(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 <code>char</code> 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</code> value. Let <code>a-d</code>
* be the first through fourth bytes read. 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 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</code> value. Let <code>a-h</code>
* be the first through eighth bytes read.
* 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 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</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 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</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 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 \u0100,
that is, (char)256.
Throws: - IOException – if an I/O error occurs.
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</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
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: - EOFException – if this stream reaches the end
before reading all the bytes.
- IOException – if an I/O error occurs.
- UTFDataFormatException – if the bytes do not represent a
valid modified UTF-8 encoding of a string.
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</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;
}