java.io
Class PushbackReader

java.lang.Object
  java.io.Reader
      java.io.FilterReader
          java.io.PushbackReader

All Implemented Interfaces:

Closeable, Readable

public class PushbackReader
extends FilterReader

A character-stream reader that allows characters to be pushed back into the stream.

Since:

JDK1.1

Field Summary

Fields inherited from class java.io.FilterReader

in

Fields inherited from class java.io.Reader

lock

Constructor Summary

PushbackReader(Reader in)
Creates a new pushback reader with a one-character pushback buffer.

PushbackReader(Reader in, int size)
Creates a new pushback reader with a pushback buffer of the given size.

Method Summary

void	close() Closes the stream and releases any system resources associated with it.
void	mark(int readAheadLimit) Marks the present position in the stream.
boolean	markSupported() Tells whether this stream supports the mark() operation, which it does not.
int	read() Reads a single character.
int	read(char[] cbuf, int off, int len) Reads characters into a portion of an array.
boolean	ready() Tells whether this stream is ready to be read.
void	reset() Resets the stream.
long	skip(long n) Skips characters.
void	unread(char[] cbuf) Pushes back an array of characters by copying it to the front of the pushback buffer.
void	unread(char[] cbuf, int off, int len) Pushes back a portion of an array of characters by copying it to the front of the pushback buffer.
void	unread(int c) Pushes back a single character by copying it to the front of the pushback buffer.

Methods inherited from class java.io.Reader

read, read

Methods inherited from class java.lang.Object

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

Constructor Detail

PushbackReader

public PushbackReader(Reader in,
                      int size)

Creates a new pushback reader with a pushback buffer of the given size.

Parameters:

in - The reader from which characters will be read

size - The size of the pushback buffer

Throws:

IllegalArgumentException - if size is <= 0

PushbackReader

public PushbackReader(Reader in)

Creates a new pushback reader with a one-character pushback buffer.

Parameters:

in - The reader from which characters will be read

Method Detail

read

public int read()
         throws IOException

Reads a single character.

Overrides:

read in class FilterReader

Returns:

The character read, or -1 if the end of the stream has been reached

Throws:

IOException - If an I/O error occurs

read

public int read(char[] cbuf,
                int off,
                int len)
         throws IOException

Reads characters into a portion of an array.

Overrides:

read in class FilterReader

Parameters:

cbuf - Destination buffer

off - Offset at which to start writing characters

len - Maximum number of characters to read

Returns:

The number of characters read, or -1 if the end of the stream has been reached

Throws:

IOException - If an I/O error occurs

unread

public void unread(int c)
            throws IOException

Pushes back a single character by copying it to the front of the pushback buffer. After this method returns, the next character to be read will have the value (char)c.

Parameters:

c - The int value representing a character to be pushed back

Throws:

IOException - If the pushback buffer is full, or if some other I/O error occurs

unread

public void unread(char[] cbuf,
                   int off,
                   int len)
            throws IOException

Pushes back a portion of an array of characters by copying it to the front of the pushback buffer. After this method returns, the next character to be read will have the value cbuf[off], the character after that will have the value cbuf[off+1], and so forth.

Parameters:

cbuf - Character array

off - Offset of first character to push back

len - Number of characters to push back

Throws:

IOException - If there is insufficient room in the pushback buffer, or if some other I/O error occurs

unread

public void unread(char[] cbuf)
            throws IOException

Pushes back an array of characters by copying it to the front of the pushback buffer. After this method returns, the next character to be read will have the value cbuf[0], the character after that will have the value cbuf[1], and so forth.

Parameters:

cbuf - Character array to push back

Throws:

IOException - If there is insufficient room in the pushback buffer, or if some other I/O error occurs

ready

public boolean ready()
              throws IOException

Tells whether this stream is ready to be read.

Overrides:

ready in class FilterReader

Returns:

True if the next read() is guaranteed not to block for input, false otherwise. Note that returning false does not guarantee that the next read will block.

Throws:

IOException - If an I/O error occurs

mark

public void mark(int readAheadLimit)
          throws IOException

Marks the present position in the stream. The mark for class PushbackReader always throws an exception.

Overrides:

mark in class FilterReader

Parameters:

readAheadLimit - Limit on the number of characters that may be read while still preserving the mark. After reading this many characters, attempting to reset the stream may fail.

Throws:

IOException - Always, since mark is not supported

reset

public void reset()
           throws IOException

Resets the stream. The reset method of PushbackReader always throws an exception.

Overrides:

reset in class FilterReader

Throws:

IOException - Always, since reset is not supported

markSupported

public boolean markSupported()

Tells whether this stream supports the mark() operation, which it does not.

Overrides:

markSupported in class FilterReader

Returns:

true if and only if this stream supports the mark operation.

close

public void close()
           throws IOException

Closes the stream and releases any system resources associated with it. Once the stream has been closed, further read(), unread(), ready(), or skip() invocations will throw an IOException. Closing a previously closed stream has no effect.

Specified by:

close in interface Closeable

Overrides:

close in class FilterReader

Throws:

IOException - If an I/O error occurs

skip

public long skip(long n)
          throws IOException

Skips characters. This method will block until some characters are available, an I/O error occurs, or the end of the stream is reached.

Overrides:

skip in class FilterReader

Parameters:

n - The number of characters to skip

Returns:

The number of characters actually skipped

Throws:

IllegalArgumentException - If n is negative.

IOException - If an I/O error occurs