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public interface DataInput
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. |
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. |
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, zero-extends it to type int , 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 |
---|
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.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.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.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.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.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.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))
This method is suitable for reading the bytes written by the
writeShort
method of interface DataOutput
.
EOFException
- if this stream reaches the end before reading all the
bytes.
IOException
- if an I/O error occurs.int readUnsignedShort() throws IOException
int
, 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
.
EOFException
- if this stream reaches the end before reading all the
bytes.
IOException
- if an I/O error occurs.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))
This method is suitable for reading bytes written by the
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.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.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.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))
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.
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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