Contents | Package | Class | Tree | Deprecated | Index | Help Java 1.2 Beta 3
PREV | NEXT SHOW LISTS | HIDE LISTS

Class java.io.PushbackInputStream

java.lang.Object
    |
    +----java.io.InputStream
            |
            +----java.io.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.

Since:
JDK1.0

Field Summary
byte[]  buf
The pushback buffer.
int  pos
The position within the pushback buffer from which the next byte will be read.
 
Fields inherited from class java.io.FilterInputStream
 in
 

Constructor Summary
 PushbackInputStream(InputStream in, int size)
Creates a new pushback input stream with a pushback buffer of the specified size.
 PushbackInputStream(InputStream in)
Creates a new pushback input stream with a one-byte pushback buffer.
 

Method Summary
int  available()
Returns the number of bytes that can be read from this input stream without blocking.
void  close()
Closes this input stream and releases any system resources associated with the stream.
boolean  markSupported()
Tests if this input stream supports the mark and reset 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 to len bytes of data from this input stream into an array of bytes.
long  skip(long n)
Skips over and discards n bytes of data from this input stream.
void  unread(int b)
Pushes back a byte 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(byte[] b)
Pushes back an array of bytes by copying it to the front of the pushback buffer.
 
Methods inherited from class java.io.FilterInputStream
 available, close, mark, markSupported, read, read, read, reset, skip
 
Methods inherited from class java.io.InputStream
 available, close, mark, markSupported, read, read, read, reset, skip
 
Methods inherited from class java.lang.Object
 clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

buf

protected byte[] buf
The pushback buffer.

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.
Constructor Detail

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.

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.
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.

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()

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

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.

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.

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.

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

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.

Parameters:
n - the number of bytes to be skipped.
Returns:
the actual number of bytes skipped.
Throws:
IOException - if an I/O error occurs.
Overrides:
skip in class FilterInputStream
See Also:
in

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()

close

public void close() throws IOException
Closes this input stream and releases any system resources associated with the stream.
Throws:
IOException - if an I/O error occurs.
Overrides:
close in class FilterInputStream

Contents | Package | Class | Tree | Deprecated | Index | Help Java 1.2 Beta 3
PREV | NEXT SHOW LISTS | HIDE LISTS

Submit a bug or feature
Submit comments/suggestions about new javadoc look.
Java is a trademark or registered trademark of Sun Microsystems, Inc. in the US and other countries.
Copyright 1993-1998 Sun Microsystems, Inc. 901 San Antonio Road, Palo Alto, California, 94303, U.S.A. All Rights Reserved.