Java™ Platform
Standard Ed. 6

java.io
Class PushbackReader

java.lang.Object
  extended by java.io.Reader
      extended by java.io.FilterReader
          extended by 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

Java™ Platform
Standard Ed. 6

Submit a bug or feature
For further API reference and developer documentation, see Java SE Developer Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.

Copyright 2008 Sun Microsystems, Inc. All rights reserved. Use is subject to license terms. Also see the documentation redistribution policy.


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