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java.base / java.io
Class PushbackReader
java.lang.Object
  java.io.Reader
      java.io.FilterReader
          java.io.PushbackReader
All Implemented Interfaces:
Closeable, AutoCloseable, Readable

public class PushbackReader
extends FilterReader
A character-stream reader that allows characters to be pushed back into the stream.
Since:
1.1
Author:
Mark Reinhold

Field Summary
Fields inherited from class java.io.FilterReader
in
Fields inherited from class java.io.Reader
lock
Constructor Summary
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
Closes the stream and releases any system resources associated with it.
void
mark(int readAheadLimit)
Marks the present position in the stream.
boolean
Tells whether this stream supports the mark() operation, which it does not.
int
Reads a single character.
int
read(char[] cbuf, int off, int len)
Reads characters into a portion of an array.
boolean
Tells whether this stream is ready to be read.
void
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
nullReader, read, read, transferTo
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 <= 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
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
Reads characters into a portion of an array. This method will block until some input is available, an I/O error occurs, or the end of the stream is reached.

If len is zero, then no characters are read and 0 is returned; otherwise, there is an attempt to read at least one character. If no character is available because the stream is at its end, the value -1 is returned; otherwise, at least one character is read and stored into cbuf.

Overrides:
read in class FilterReader
Parameters:
cbuf - Destination buffer
off - Offset at which to start storing 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
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
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
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
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
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
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
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. This method will block while there is another thread blocking on the reader.
Specified by:
close in interface Closeable
close in interface AutoCloseable
Overrides:
close in class FilterReader
Throws:
IOException - If an I/O error occurs

skip
public long skip
(long n)
throws
Skips characters. This method will block until some characters are available, an I/O error occurs, or the end of the stream is reached. If the stream is already at its end before this method is invoked, then no characters are skipped and zero is returned.
Overrides:
skip in class FilterReader
Parameters:
n - The number of characters to skip
Returns:
The number of characters actually skipped
Throws:
IOException - If an I/O error occurs

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