java.lang.Object | |||
↳ | java.io.InputStream | ||
↳ | java.io.FilterInputStream | ||
↳ | java.io.PushbackInputStream |
A PushbackInputStream
adds
functionality to another input stream, namely
the ability to "push back" or "unread"
one byte. This is useful in situations where
it is convenient for a fragment of code
to read an indefinite number of data bytes
that are delimited by a particular byte
value; after reading the terminating byte,
the code fragment can "unread" it, so that
the next read operation on the input stream
will reread the byte that was pushed back.
For example, bytes representing the characters
constituting an identifier might be terminated
by a byte representing an operator character;
a method whose job is to read just an identifier
can read until it sees the operator and
then push the operator back to be re-read.
Fields | |||||||||||
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buf | The pushback buffer. | ||||||||||
pos | The position within the pushback buffer from which the next byte will be read. |
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Inherited Fields | |||||||||||
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From class
java.io.FilterInputStream
|
Public Constructors | |||||||||||
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Creates a
PushbackInputStream
with a pushback buffer of the specified size ,
and saves its argument, the input stream
in , for later use. | |||||||||||
Creates a
PushbackInputStream
and saves its argument, the input stream
in , for later use. |
Public Methods | |||||||||||
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Returns an estimate of the number of bytes that can be read (or
skipped over) from this input stream without blocking by the next
invocation of a method for this input stream.
| |||||||||||
Closes this input stream and releases any system resources
associated with the stream.
| |||||||||||
Marks the current position in this input stream.
| |||||||||||
Tests if this input stream supports the
mark and
reset methods, which it does not. | |||||||||||
Reads the next byte of data from this input stream.
| |||||||||||
Reads up to
len bytes of data from this input stream into
an array of bytes. | |||||||||||
Repositions this stream to the position at the time the
mark method was last called on this input stream. | |||||||||||
Skips over and discards
n bytes of data from this
input stream. | |||||||||||
Pushes back a portion of an array of bytes by copying it to the front
of the pushback buffer.
| |||||||||||
Pushes back an array of bytes by copying it to the front of the
pushback buffer.
| |||||||||||
Pushes back a byte by copying it to the front of the pushback buffer.
|
[Expand]
Inherited Methods | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
From class
java.io.FilterInputStream
| |||||||||||
From class
java.io.InputStream
| |||||||||||
From class
java.lang.Object
| |||||||||||
From interface
java.io.Closeable
|
The pushback buffer.
The position within the pushback buffer from which the next byte will
be read. When the buffer is empty, pos
is equal to
buf.length
; when the buffer is full, pos
is
equal to zero.
Creates a PushbackInputStream
with a pushback buffer of the specified size
,
and saves its argument, the input stream
in
, for later use. Initially,
there is no pushed-back byte (the field
pushBack
is initialized to
-1
).
in | the input stream from which bytes will be read. |
---|---|
size | the size of the pushback buffer. |
IllegalArgumentException | if size is <= 0 |
---|
Creates a PushbackInputStream
and saves its argument, the input stream
in
, for later use. Initially,
there is no pushed-back byte (the field
pushBack
is initialized to
-1
).
in | the input stream from which bytes will be read. |
---|
Returns an estimate of the number of bytes that can be read (or skipped over) from this input stream without blocking by the next invocation of a method for this input stream. The next invocation might be the same thread or another thread. A single read or skip of this many bytes will not block, but may read or skip fewer bytes.
The method returns the sum of the number of bytes that have been
pushed back and the value returned by available
.
IOException | if this input stream has been closed by
invoking its close() method,
or an I/O error occurs. |
---|
Closes this input stream and releases any system resources associated with the stream. Once the stream has been closed, further read(), unread(), available(), reset(), or skip() invocations will throw an IOException. Closing a previously closed stream has no effect.
IOException | if an I/O error occurs. |
---|
Marks the current position in this input stream.
The mark
method of PushbackInputStream
does nothing.
readlimit | the maximum limit of bytes that can be read before the mark position becomes invalid. |
---|
Reads the next byte of data from this input stream. The value
byte is returned as an int
in the range
0
to 255
. If no byte is available
because the end of the stream has been reached, the value
-1
is returned. This method blocks until input data
is available, the end of the stream is detected, or an exception
is thrown.
This method returns the most recently pushed-back byte, if there is
one, and otherwise calls the read
method of its underlying
input stream and returns whatever value that method returns.
-1
if the end of the
stream has been reached.IOException | if this input stream has been closed by
invoking its close() method,
or an I/O error occurs. |
---|
Reads up to len
bytes of data from this input stream into
an array of bytes. This method first reads any pushed-back bytes; after
that, if fewer than len
bytes have been read then it
reads from the underlying input stream. If len
is not zero, the method
blocks until at least 1 byte of input is available; otherwise, no
bytes are read and 0
is returned.
b | the buffer into which the data is read. |
---|---|
off | the start offset in the destination array b |
len | the maximum number of bytes read. |
-1
if there is no more data because the end of
the stream has been reached.NullPointerException | If b is null . |
---|---|
IndexOutOfBoundsException | If off is negative,
len is negative, or len is greater than
b.length - off |
IOException | if this input stream has been closed by
invoking its close() method,
or an I/O error occurs. |
Repositions this stream to the position at the time the
mark
method was last called on this input stream.
The method reset
for class
PushbackInputStream
does nothing except throw an
IOException
.
IOException | if this method is invoked. |
---|
Skips over and discards n
bytes of data from this
input stream. The skip
method may, for a variety of
reasons, end up skipping over some smaller number of bytes,
possibly zero. If n
is negative, no bytes are skipped.
The skip
method of PushbackInputStream
first skips over the bytes in the pushback buffer, if any. It then
calls the skip
method of the underlying input stream if
more bytes need to be skipped. The actual number of bytes skipped
is returned.
n |
---|
IOException | if the stream does not support seek,
or the stream has been closed by
invoking its close() method,
or an I/O error occurs. |
---|
Pushes back a portion of an array of bytes by copying it to the front
of the pushback buffer. After this method returns, the next byte to be
read will have the value b[off]
, the byte after that will
have the value b[off+1]
, and so forth.
b | the byte array to push back. |
---|---|
off | the start offset of the data. |
len | the number of bytes to push back. |
IOException | If there is not enough room in the pushback
buffer for the specified number of bytes,
or this input stream has been closed by
invoking its close() method. |
---|
Pushes back an array of bytes by copying it to the front of the
pushback buffer. After this method returns, the next byte to be read
will have the value b[0]
, the byte after that will have the
value b[1]
, and so forth.
b | the byte array to push back |
---|
IOException | If there is not enough room in the pushback
buffer for the specified number of bytes,
or this input stream has been closed by
invoking its close() method. |
---|
Pushes back a byte by copying it to the front of the pushback buffer.
After this method returns, the next byte to be read will have the value
(byte)b
.
b | the int value whose low-order
byte is to be pushed back. |
---|
IOException | If there is not enough room in the pushback
buffer for the byte, or this input stream has been closed by
invoking its close() method.
|
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