java.io

Class PushbackReader

java.lang.Object

java.io.Reader

java.io.FilterReader

java.io.PushbackReader

All Implemented Interfaces:

Closeable

public class PushbackReader
extends FilterReader

This subclass of FilterReader provides the ability to unread data from a stream. It maintains an internal buffer of unread data that is supplied to the next read operation. This is conceptually similar to mark/reset functionality, except that in this case the position to reset the stream to does not need to be known in advance.

The default pushback buffer size one char, but this can be overridden by the creator of the stream.

Author:

Aaron M. Renn (arenn@urbanophile.com), Warren Levy (warrenl@cygnus.com)

Constructor Summary

Constructors

Constructor and Description
PushbackReader(Reader in) This method initializes a PushbackReader to read from the specified subordinate Reader with a default pushback buffer size of 1.
PushbackReader(Reader in, int bufsize) This method initializes a PushbackReader to read from the specified subordinate Reader with the specified buffer size

Method Summary

Modifier and Type	Method and Description
void	close() This method closes the stream and frees any associated resources.
void	mark(int read_limit) This method throws an exception when called since this class does not support mark/reset.
boolean	markSupported() This method returns false to indicate that it does not support mark/reset functionality.
int	read() This method reads an unsigned char from the input stream and returns it as an int in the range of 0-65535.
int	read(char[] buffer, int offset, int length) This method read chars from a stream and stores them into a caller supplied buffer.
boolean	ready() This method determines whether or not this stream is ready to be read.
void	reset() This method always throws an IOException in this class because mark/reset functionality is not supported.
long	skip(long num_chars) This method skips the specified number of chars in the stream.
void	unread(char[] buf) This method pushes all of the chars in the passed char array into the pushback buffer.
void	unread(char[] buffer, int offset, int length) This method pushed back chars from the passed in array into the pushback buffer.
void	unread(int b) This method pushes a single char of data into the pushback buffer.

Methods inherited from class java.io.Reader

read

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

PushbackReader

public PushbackReader(Reader in)

This method initializes a PushbackReader to read from the specified subordinate Reader with a default pushback buffer size of 1.

Parameters:

in - The subordinate stream to read from

PushbackReader

public PushbackReader(Reader in,
                      int bufsize)

This method initializes a PushbackReader to read from the specified subordinate Reader with the specified buffer size

Parameters:

in - The subordinate Reader to read from

bufsize - The pushback buffer size to use

Method Detail

close

public void close()
           throws IOException

This method closes the stream and frees any associated resources.

Specified by:

close in interface Closeable

Overrides:

close in class FilterReader

Throws:

IOException - If an error occurs.

mark

public void mark(int read_limit)
          throws IOException

This method throws an exception when called since this class does not support mark/reset.

Overrides:

mark in class FilterReader

Parameters:

read_limit - Not used.

Throws:

IOException - Always thrown to indicate mark/reset not supported.

markSupported

public boolean markSupported()

This method returns false to indicate that it does not support mark/reset functionality.

Overrides:

markSupported in class FilterReader

Returns:

This method returns false to indicate that this class does not support mark/reset functionality

read

public int read()
         throws IOException

This method reads an unsigned char from the input stream and returns it as an int in the range of 0-65535. This method also will return -1 if the end of the stream has been reached. The char returned will be read from the pushback buffer, unless the buffer is empty, in which case the char will be read from the underlying stream.

This method will block until the char can be read.

Overrides:

read in class FilterReader

Returns:

The char read or -1 if end of stream

Throws:

IOException - If an error occurs

read

public int read(char[] buffer,
                int offset,
                int length)
         throws IOException

This method read chars from a stream and stores them into a caller supplied buffer. It starts storing the data at index offset into the buffer and attempts to read len chars. This method can return before reading the number of chars requested. The actual number of chars read is returned as an int. A -1 is returned to indicate the end of the stream.

This method will block until some data can be read.

This method first reads chars from the pushback buffer in order to satisfy the read request. If the pushback buffer cannot provide all of the chars requested, the remaining chars are read from the underlying stream.

Overrides:

read in class FilterReader

Parameters:

buffer - The array into which the chars read should be stored

offset - The offset into the array to start storing chars

length - The requested number of chars to read

Returns:

The actual number of chars read, or -1 if end of stream.

Throws:

IOException - If an error occurs.

ready

public boolean ready()
              throws IOException

This method determines whether or not this stream is ready to be read. If it returns false to indicate that the stream is not ready, any attempt to read from the stream could (but is not guaranteed to) block.

This stream is ready to read if there are either chars waiting to be read in the pushback buffer or if the underlying stream is ready to be read.

Overrides:

ready in class FilterReader

Returns:

true if this stream is ready to be read, false otherwise

Throws:

IOException - If an error occurs

reset

public void reset()
           throws IOException

This method always throws an IOException in this class because mark/reset functionality is not supported.

Overrides:

reset in class FilterReader

Throws:

IOException - Always thrown for this class

skip

public long skip(long num_chars)
          throws IOException

This method skips the specified number of chars in the stream. It returns the actual number of chars skipped, which may be less than the requested amount.

This method first discards chars from the buffer, then calls the skip method on the underlying Reader to skip additional chars if necessary.

Overrides:

skip in class FilterReader

Parameters:

num_chars - The requested number of chars to skip

Returns:

The actual number of chars skipped.

Throws:

IOException - If an error occurs

unread

public void unread(char[] buf)
            throws IOException

This method pushes all of the chars in the passed char array into the pushback buffer. These chars are pushed in reverse order so that the next char read from the stream after this operation will be buf[0] followed by buf[1], etc.

If the pushback buffer cannot hold all of the requested chars, an exception is thrown.

Parameters:

buf - The char array to be pushed back

Throws:

IOException - If the pushback buffer is full

unread

public void unread(char[] buffer,
                   int offset,
                   int length)
            throws IOException

This method pushed back chars from the passed in array into the pushback buffer. The chars from buf[offset] to buf[offset + len] are pushed in reverse order so that the next char read from the stream after this operation will be buf[offset] followed by buf[offset + 1], etc.

If the pushback buffer cannot hold all of the requested chars, an exception is thrown.

Parameters:

buffer - The char array to be pushed back

offset - The index into the array where the chars to be push start

length - The number of chars to be pushed.

Throws:

IOException - If the pushback buffer is full

unread

public void unread(int b)
            throws IOException

This method pushes a single char of data into the pushback buffer. The char pushed back is the one that will be returned as the first char of the next read.

If the pushback buffer is full, this method throws an exception.

The argument to this method is an int. Only the low eight bits of this value are pushed back.

Parameters:

b - The char to be pushed back, passed as an int

Throws:

IOException - If the pushback buffer is full.