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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 Java 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.
DataInputStream,
DataOutput| Method Summary | |
boolean |
readBoolean()
Reads one input byte and returns true if that byte is nonzero,
false if that byte is zero.
|
byte |
readByte()
Reads and returns one input byte. |
char |
readChar()
Reads an input char and returns the char value.
|
double |
readDouble()
Reads eight input bytes and returns a double value. |
float |
readFloat()
Reads four input bytes and returns a float value. |
void |
readFully(byte[] b)
Reads some bytes from an input stream and stores them into the buffer array b. |
void |
readFully(byte[] b,
int off,
int len)
Reads len
bytes from
an input stream.
|
int |
readInt()
Reads four input bytes and returns an int value. |
String |
readLine()
Reads the next line of text from the input stream. |
long |
readLong()
Reads eight input bytes and returns a long value. |
short |
readShort()
Reads two input bytes and returns a short value. |
int |
readUnsignedByte()
Reads one input byte, zero-extends it to type int, and returns
the result, which is therefore in the range
0
through 255.
|
int |
readUnsignedShort()
Reads two input bytes and returns an int value in the range 0
through 65535. |
String |
readUTF()
Reads in a string that has been encoded using a modified UTF-8 format. |
int |
skipBytes(int n)
Makes an attempt to skip over n bytes
of data from the input
stream, discarding the skipped bytes. |
| Method Detail |
public void readFully(byte[] b)
throws IOException
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.
EOFException
is thrown.
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.
b - the buffer into which the data is read.
EOFException - if this stream reaches the end before reading
all the bytes.
IOException - if an I/O error occurs.
public void readFully(byte[] b,
int off,
int len)
throws IOException
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.
EOFException
is thrown.
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.
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.
EOFException - if this stream reaches the end before reading
all the bytes.
IOException - if an I/O error occurs.
public int skipBytes(int n)
throws IOException
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.
n - the number of bytes to be skipped.
IOException - if an I/O error occurs.
public boolean readBoolean()
throws IOException
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.
boolean value read.
EOFException - if this stream reaches the end before reading
all the bytes.
IOException - if an I/O error occurs.
public byte readByte()
throws IOException
-128 through 127,
inclusive.
This method is suitable for
reading the byte written by the writeByte
method of interface DataOutput.
EOFException - if this stream reaches the end before reading
all the bytes.
IOException - if an I/O error occurs.
public int readUnsignedByte()
throws IOException
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.
EOFException - if this stream reaches the end before reading
all the bytes.
IOException - if an I/O error occurs.
public short readShort()
throws IOException
short value. Let a
be the first byte read and b
be the second byte. The value
returned
is:
(short)((a << 8) * | (b & 0xff))
writeShort method of
interface DataOutput.
EOFException - if this stream reaches the end before reading
all the bytes.
IOException - if an I/O error occurs.
public int readUnsignedShort()
throws IOException
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))
writeShort method
of interface DataOutput if
the argument to writeShort
was intended to be a value in the range
0 through 65535.
EOFException - if this stream reaches the end before reading
all the bytes.
IOException - if an I/O error occurs.
public char readChar()
throws IOException
char and returns the char value.
A Unicode char is made up of two bytes.
Let a
be the first byte read and b
be the second byte. The value
returned is:
(char)((a << 8) | (b & 0xff))
writeChar method of interface
DataOutput.
char read.
EOFException - if this stream reaches the end before reading
all the bytes.
IOException - if an I/O error occurs.
public int readInt()
throws IOException
int value. Let a
be the first byte read, b be
the second byte, c be the third
byte,
and d be the fourth
byte. 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.
int value read.
EOFException - if this stream reaches the end before reading
all the bytes.
IOException - if an I/O error occurs.
public long readLong()
throws IOException
long value. Let a
be the first byte read, b be
the second byte, c be the third
byte, d
be the fourth byte,
e be the fifth byte, f
be the sixth byte, g be the
seventh byte,
and h be the
eighth byte. 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.
long value read.
EOFException - if this stream reaches the end before reading
all the bytes.
IOException - if an I/O error occurs.
public float readFloat()
throws IOException
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.
float value read.
EOFException - if this stream reaches the end before reading
all the bytes.
IOException - if an I/O error occurs.
public double readDouble()
throws IOException
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.
double value read.
EOFException - if this stream reaches the end before reading
all the bytes.
IOException - if an I/O error occurs.
public String readLine()
throws IOException
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.
null if the end of file is
encountered before a byte can be read.
IOException - if an I/O error occurs.
public String readUTF()
throws IOException
readUTF
is that it reads a representation of a Unicode
character string encoded in Java 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))
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))
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.
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 UTF-8 encoding of a string.
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