Class PushbackInputStream
java.lang.Object
java.io.InputStream
java.io.FilterInputStream
java.io.PushbackInputStream
- All Implemented Interfaces:
Closeable
,AutoCloseable
A
PushbackInputStream
adds
functionality to another input stream, namely
the ability to "push back" or "unread" bytes,
by storing pushed-back bytes in an internal buffer.
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.- Since:
- 1.0
-
Field Summary
Modifier and TypeFieldDescriptionprotected byte[]
The pushback buffer.protected int
The position within the pushback buffer from which the next byte will be read.Fields declared in class java.io.FilterInputStream
in
-
Constructor Summary
ConstructorDescriptionCreates aPushbackInputStream
with a 1-byte pushback buffer, and saves its argument, the input streamin
, for later use.PushbackInputStream
(InputStream in, int size) Creates aPushbackInputStream
with a pushback buffer of the specifiedsize
, and saves its argument, the input streamin
, for later use. -
Method Summary
Modifier and TypeMethodDescriptionint
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.void
close()
Closes this input stream and releases any system resources associated with the stream.void
mark
(int readlimit) Marks the current position in this input stream.boolean
Tests if this input stream supports themark
andreset
methods, which it does not.int
read()
Reads the next byte of data from this input stream.int
read
(byte[] b, int off, int len) Reads up tolen
bytes of data from this input stream into an array of bytes.void
reset()
Repositions this stream to the position at the time themark
method was last called on this input stream.long
skip
(long n) Skips over and discardsn
bytes of data from this input stream.void
unread
(byte[] b) Pushes back an array of bytes by copying it to the front of the pushback buffer.void
unread
(byte[] b, int off, int len) Pushes back a portion of an array of bytes by copying it to the front of the pushback buffer.void
unread
(int b) Pushes back a byte by copying it to the front of the pushback buffer.Methods declared in class java.io.FilterInputStream
read
Methods declared in class java.io.InputStream
nullInputStream, readAllBytes, readNBytes, readNBytes, skipNBytes, transferTo
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Field Details
-
buf
protected byte[] bufThe pushback buffer.- Since:
- 1.1
-
pos
protected int posThe position within the pushback buffer from which the next byte will be read. When the buffer is empty,pos
is equal tobuf.length
; when the buffer is full,pos
is equal to zero.- Since:
- 1.1
-
-
Constructor Details
-
PushbackInputStream
Creates aPushbackInputStream
with a pushback buffer of the specifiedsize
, and saves its argument, the input streamin
, for later use. Initially, the pushback buffer is empty.- Parameters:
in
- the input stream from which bytes will be read.size
- the size of the pushback buffer.- Throws:
IllegalArgumentException
- ifsize <= 0
- Since:
- 1.1
-
PushbackInputStream
Creates aPushbackInputStream
with a 1-byte pushback buffer, and saves its argument, the input streamin
, for later use. Initially, the pushback buffer is empty.- Parameters:
in
- the input stream from which bytes will be read.
-
-
Method Details
-
read
Reads the next byte of data from this input stream. The value byte is returned as anint
in the range0
to255
. 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.- Overrides:
read
in classFilterInputStream
- Returns:
- the next byte of data, or
-1
if the end of the stream has been reached. - Throws:
IOException
- if this input stream has been closed by invoking itsclose()
method, or an I/O error occurs.- See Also:
-
read
Reads up tolen
bytes of data from this input stream into an array of bytes. This method first reads any pushed-back bytes; after that, if fewer thanlen
bytes have been read then it reads from the underlying input stream. Iflen
is not zero, the method blocks until at least 1 byte of input is available; otherwise, no bytes are read and0
is returned.- Overrides:
read
in classFilterInputStream
- Parameters:
b
- the buffer into which the data is read.off
- the start offset in the destination arrayb
len
- the maximum number of bytes read.- Returns:
- the total number of bytes read into the buffer, or
-1
if there is no more data because the end of the stream has been reached. - Throws:
NullPointerException
- Ifb
isnull
.IndexOutOfBoundsException
- Ifoff
is negative,len
is negative, orlen
is greater thanb.length - off
IOException
- if this input stream has been closed by invoking itsclose()
method, or an I/O error occurs.- See Also:
-
unread
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
.- Parameters:
b
- theint
value whose low-order byte is to be pushed back.- Throws:
IOException
- If there is not enough room in the pushback buffer for the byte, or this input stream has been closed by invoking itsclose()
method.
-
unread
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 valueb[off]
, the byte after that will have the valueb[off+1]
, and so forth.- Parameters:
b
- the byte array to push back.off
- the start offset of the data.len
- the number of bytes to push back.- Throws:
NullPointerException
- Ifb
isnull
.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 itsclose()
method.- Since:
- 1.1
-
unread
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 valueb[0]
, the byte after that will have the valueb[1]
, and so forth.- Parameters:
b
- the byte array to push back- Throws:
NullPointerException
- Ifb
isnull
.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 itsclose()
method.- Since:
- 1.1
-
available
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
.- Overrides:
available
in classFilterInputStream
- Returns:
- the number of bytes that can be read (or skipped over) from the input stream without blocking.
- Throws:
IOException
- if this input stream has been closed by invoking itsclose()
method, or an I/O error occurs.- See Also:
-
skip
Skips over and discardsn
bytes of data from this input stream. Theskip
method may, for a variety of reasons, end up skipping over some smaller number of bytes, possibly zero. Ifn
is negative, no bytes are skipped.The
skip
method ofPushbackInputStream
first skips over the bytes in the pushback buffer, if any. It then calls theskip
method of the underlying input stream if more bytes need to be skipped. The actual number of bytes skipped is returned.- Overrides:
skip
in classFilterInputStream
- Parameters:
n
- the number of bytes to be skipped.- Returns:
- the actual number of bytes skipped.
- Throws:
IOException
- if the stream has been closed by invoking itsclose()
method,in.skip(n)
throws an IOException, or an I/O error occurs.- Since:
- 1.2
- See Also:
-
markSupported
public boolean markSupported()Tests if this input stream supports themark
andreset
methods, which it does not.- Overrides:
markSupported
in classFilterInputStream
- Returns:
false
, since this class does not support themark
andreset
methods.- See Also:
-
mark
public void mark(int readlimit) Marks the current position in this input stream.The
mark
method ofPushbackInputStream
does nothing.- Overrides:
mark
in classFilterInputStream
- Parameters:
readlimit
- the maximum limit of bytes that can be read before the mark position becomes invalid.- See Also:
-
reset
Repositions this stream to the position at the time themark
method was last called on this input stream.The method
reset
for classPushbackInputStream
does nothing except throw anIOException
.- Overrides:
reset
in classFilterInputStream
- Throws:
IOException
- if this method is invoked.- See Also:
-
close
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.- Specified by:
close
in interfaceAutoCloseable
- Specified by:
close
in interfaceCloseable
- Overrides:
close
in classFilterInputStream
- Throws:
IOException
- if an I/O error occurs.- See Also:
-