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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

Field Summary

Fields declared in class java.io.FilterReader

in

Fields declared in class java.io.Reader

lock

Constructor Summary

Constructor	Description
`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

Modifier and Type	Method	Description
`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.
`boolean`	`ready()`	Tells whether this stream is ready to be read.
`void`	`reset()`	Resets the stream.
`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 declared in class java.io.FilterReader

read, skip

Methods declared in class java.io.Reader

nullReader, read, read, transferTo

Methods declared in class java.lang.Object

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

Constructor Details

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 Details

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

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. This method will block while there is another thread blocking on the reader.

Specified by:: close in interface AutoCloseable
Specified by:: close in interface Closeable
Specified by:: close in class Reader
Throws:: IOException - If an I/O error occurs

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Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
Various third party code in OpenJDK is licensed under different licenses (see Debian package).
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https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/io/PushbackReader.html