Class PushbackInputStream
- java.lang.Object
-
- java.io.InputStream
-
- java.io.FilterInputStream
-
- java.io.PushbackInputStream
- All Implemented Interfaces:
-
Closeable
,AutoCloseable
public class PushbackInputStream extends FilterInputStream
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 Type | Field | Description |
---|---|---|
protected byte[] | buf | The pushback buffer. |
protected int | pos | The position within the pushback buffer from which the next byte will be read. |
Fields declared in class java.io.FilterInputStream
in
Constructor Summary
Constructor | Description |
---|---|
PushbackInputStream(InputStream in) | Creates a |
PushbackInputStream(InputStream in,
int size) | Creates a |
Method Summary
Modifier and Type | Method | Description |
---|---|---|
int | 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. |
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 | markSupported() | Tests if this input stream supports the |
int | read() | Reads the next byte of data from this input stream. |
int | read(byte[] b,
int off,
int len) | Reads up to |
void | reset() | Repositions this stream to the position at the time the |
long | skip(long n) | Skips over and discards |
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, transferTo
Methods declared in class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
Field Detail
buf
protected byte[] buf
The pushback buffer.
- Since:
- 1.1
pos
protected int pos
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.
- Since:
- 1.1
Constructor Detail
PushbackInputStream
public PushbackInputStream(InputStream in, int size)
Creates a PushbackInputStream
with a pushback buffer of the specified size
, and saves its argument, the input stream in
, 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
public PushbackInputStream(InputStream in)
Creates a PushbackInputStream
with a 1-byte pushback buffer, and saves its argument, the input stream in
, for later use. Initially, the pushback buffer is empty.
- Parameters:
-
in
- the input stream from which bytes will be read.
Method Detail
read
public int read() throws IOException
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.
- 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:
InputStream.read()
read
public int read(byte[] b, int off, int len) throws IOException
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.
- 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:
InputStream.read(byte[], int, int)
unread
public void unread(int b) throws IOException
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
public void unread(byte[] b, int off, int len) throws IOException
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.
- Parameters:
-
b
- the byte array to push back. -
off
- the start offset of the data. -
len
- the number of bytes to push back. - Throws:
-
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
public void unread(byte[] b) throws IOException
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.
- Parameters:
-
b
- the byte array to push back - Throws:
-
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
public int available() throws IOException
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:
-
FilterInputStream.in
,InputStream.available()
skip
public long skip(long n) throws IOException
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.
- 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:
-
FilterInputStream.in
,InputStream.skip(long n)
markSupported
public boolean markSupported()
Tests if this input stream supports the mark
and reset
methods, which it does not.
- Overrides:
-
markSupported
in classFilterInputStream
- Returns:
-
false
, since this class does not support themark
andreset
methods. - See Also:
-
InputStream.mark(int)
,InputStream.reset()
mark
public void mark(int readlimit)
Marks the current position in this input stream.
The mark
method of PushbackInputStream
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:
InputStream.reset()
reset
public void reset() throws IOException
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
.
- Overrides:
-
reset
in classFilterInputStream
- Throws:
-
IOException
- if this method is invoked. - See Also:
-
InputStream.mark(int)
,IOException
close
public void close() throws IOException
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:
FilterInputStream.in