Class java.io.PushbackInputStream 
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Class java.io.PushbackInputStream 

Object
   |
   +----InputStream
           |
           +----FilterInputStream
                   |
                   +----java.io.PushbackInputStream
public class PushbackInputStream
extends FilterInputStream
This class is an input stream filter that provides a buffer into which data can be "unread." An application may unread data at any time by pushing it back into the buffer, as long as the buffer has sufficient room. Subsequent reads will read all of the pushed-back data in the buffer before reading from the underlying input stream.

This functionality is useful when a fragment of code should read an indefinite number of data bytes that are delimited by particular byte values. After reading the terminating byte the code fragment can push it back, so that the next read operation on the input stream will re-read that byte.

Version:
1.17, 07/01/98
Author:
David Connelly, Jonathan Payne
Since:
JDK1.0

Variable Index

o buf
The pushback buffer.
o pos
The position within the pushback buffer from which the next byte will be read.

Constructor Index

o java.io.PushbackInputStream(InputStream, int)
Creates a new pushback input stream with a pushback buffer of the specified size.
o java.io.PushbackInputStream(InputStream)
Creates a new pushback input stream with a one-byte pushback buffer.

Method Index

o available()
Returns the number of bytes that can be read from this input stream without blocking.
o markSupported()
Tests if this input stream supports the mark and reset methods, which it does not.
o read()
Reads the next byte of data from this input stream.
o read(byte[], int, int)
Reads up to len bytes of data from this input stream into an array of bytes.
o unread(int)
Pushes back a byte by copying it to the front of the pushback buffer.
o unread(byte[], int, int)
Pushes back a portion of an array of bytes by copying it to the front of the pushback buffer.
o unread(byte[])
Pushes back an array of bytes by copying it to the front of the pushback buffer.

Variables

o buf 
protected byte[] buf
The pushback buffer.

Since: JDK1.1
o 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: JDK1.1

Constructors

o PushbackInputStream 
public PushbackInputStream(InputStream in,
                           int size)
Creates a new pushback input stream with a pushback buffer of the specified size.

Parameters:
in - the input stream from which bytes will be read.
size - the size of the pushback buffer.
Since:
JDK1.1
o PushbackInputStream 
public PushbackInputStream(InputStream in)
Creates a new pushback input stream with a one-byte pushback buffer.

Parameters:
in - the input stream from which bytes will be read.

Methods

o available 
public int available() throws IOException
Returns the number of bytes that can be read from this input stream without blocking. This method calls the available method of the underlying input stream; it returns that value plus the number of bytes that have been pushed back.

Returns:
the number of bytes that can be read from the input stream without blocking.
Throws: IOException
if an I/O error occurs.
Overrides:
available in class FilterInputStream
See Also:
in
o markSupported 
public boolean markSupported()
Tests if this input stream supports the mark and reset methods, which it does not.

Returns:
false, since this class does not support the mark and reset methods.
Overrides:
markSupported in class FilterInputStream
See Also:
mark(int), reset()
o 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.

Returns:
the next byte of data, or -1 if the end of the stream has been reached.
Throws: IOException
if an I/O error occurs.
Overrides:
read in class FilterInputStream
See Also:
read()
o 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 than len bytes have been read then it reads from the underlying input stream. This method blocks until at least 1 byte of input is available.

Parameters:
b - the buffer into which the data is read.
off - the start offset of the data.
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: IOException
if an I/O error occurs.
Overrides:
read in class FilterInputStream
o 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 - the int 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.
o 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.
Since:
JDK1.1
o 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.
Since:
JDK1.1 
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