PushbackReader (Java Platform SE 8 ) (original) (raw)

• 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:
JDK1.1

• • Field Summary

     * ### Fields inherited from class java.io.[FilterReader](../../java/io/FilterReader.html "class in java.io")  
     `[in](../../java/io/FilterReader.html#in)`  
     * ### Fields inherited from class java.io.[Reader](../../java/io/Reader.html "class in java.io")  
     `[lock](../../java/io/Reader.html#lock)`  

  • Constructor Summary

  Constructors

  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

  All Methods Instance Methods Concrete Methods

  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.
  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](../../java/io/Reader.html "class in java.io")  
     `[read](../../java/io/Reader.html#read-char:A-), [read](../../java/io/Reader.html#read-java.nio.CharBuffer-)`  
     * ### Methods inherited from class java.lang.[Object](../../java/lang/Object.html "class in java.lang")  
     `[clone](../../java/lang/Object.html#clone--), [equals](../../java/lang/Object.html#equals-java.lang.Object-), [finalize](../../java/lang/Object.html#finalize--), [getClass](../../java/lang/Object.html#getClass--), [hashCode](../../java/lang/Object.html#hashCode--), [notify](../../java/lang/Object.html#notify--), [notifyAll](../../java/lang/Object.html#notifyAll--), [toString](../../java/lang/Object.html#toString--), [wait](../../java/lang/Object.html#wait--), [wait](../../java/lang/Object.html#wait-long-), [wait](../../java/lang/Object.html#wait-long-int-)`

• • Constructor Detail

     * #### PushbackReader  
     public PushbackReader([Reader](../../java/io/Reader.html "class in java.io") 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](../../java/lang/IllegalArgumentException.html "class in java.lang")` \- if `size <= 0`  
     * #### PushbackReader  
     public PushbackReader([Reader](../../java/io/Reader.html "class in java.io") 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](../../java/io/IOException.html "class in java.io")  
    Reads a single character.  
    Overrides:  
    `[read](../../java/io/FilterReader.html#read--)` in class `[FilterReader](../../java/io/FilterReader.html "class in java.io")`  
    Returns:  
    The character read, or -1 if the end of the stream has been reached  
    Throws:  
    `[IOException](../../java/io/IOException.html "class in java.io")` \- If an I/O error occurs  
    * #### read  
    public int read(char[] cbuf,  
                    int off,  
                    int len)  
             throws [IOException](../../java/io/IOException.html "class in java.io")  
    Reads characters into a portion of an array.  
    Overrides:  
    `[read](../../java/io/FilterReader.html#read-char:A-int-int-)` in class `[FilterReader](../../java/io/FilterReader.html "class in java.io")`  
    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](../../java/io/IOException.html "class in java.io")` \- If an I/O error occurs  
    * #### unread  
    public void unread(int c)  
                throws [IOException](../../java/io/IOException.html "class in java.io")  
    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](../../java/io/IOException.html "class in java.io")` \- 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](../../java/io/IOException.html "class in java.io")  
    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](../../java/io/IOException.html "class in java.io")` \- 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](../../java/io/IOException.html "class in java.io")  
    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](../../java/io/IOException.html "class in java.io")` \- If there is insufficient room in the pushback buffer, or if some other I/O error occurs  
    * #### ready  
    public boolean ready()  
                  throws [IOException](../../java/io/IOException.html "class in java.io")  
    Tells whether this stream is ready to be read.  
    Overrides:  
    `[ready](../../java/io/FilterReader.html#ready--)` in class `[FilterReader](../../java/io/FilterReader.html "class in java.io")`  
    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](../../java/io/IOException.html "class in java.io")` \- If an I/O error occurs  
    * #### mark  
    public void mark(int readAheadLimit)  
              throws [IOException](../../java/io/IOException.html "class in java.io")  
    Marks the present position in the stream. The `mark` for class `PushbackReader` always throws an exception.  
    Overrides:  
    `[mark](../../java/io/FilterReader.html#mark-int-)` in class `[FilterReader](../../java/io/FilterReader.html "class in java.io")`  
    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](../../java/io/IOException.html "class in java.io")` \- Always, since mark is not supported  
    * #### reset  
    public void reset()  
               throws [IOException](../../java/io/IOException.html "class in java.io")  
    Resets the stream. The `reset` method of`PushbackReader` always throws an exception.  
    Overrides:  
    `[reset](../../java/io/FilterReader.html#reset--)` in class `[FilterReader](../../java/io/FilterReader.html "class in java.io")`  
    Throws:  
    `[IOException](../../java/io/IOException.html "class in java.io")` \- Always, since reset is not supported  
    * #### markSupported  
    public boolean markSupported()  
    Tells whether this stream supports the mark() operation, which it does not.  
    Overrides:  
    `[markSupported](../../java/io/FilterReader.html#markSupported--)` in class `[FilterReader](../../java/io/FilterReader.html "class in java.io")`  
    Returns:  
    true if and only if this stream supports the mark operation.  
    * #### close  
    public void close()  
               throws [IOException](../../java/io/IOException.html "class in java.io")  
    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](../../java/io/Closeable.html#close--)` in interface `[Closeable](../../java/io/Closeable.html "interface in java.io")`  
    Specified by:  
    `[close](../../java/lang/AutoCloseable.html#close--)` in interface `[AutoCloseable](../../java/lang/AutoCloseable.html "interface in java.lang")`  
    Overrides:  
    `[close](../../java/io/FilterReader.html#close--)` in class `[FilterReader](../../java/io/FilterReader.html "class in java.io")`  
    Throws:  
    `[IOException](../../java/io/IOException.html "class in java.io")` \- If an I/O error occurs  
    * #### skip  
    public long skip(long n)  
              throws [IOException](../../java/io/IOException.html "class in java.io")  
    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](../../java/io/FilterReader.html#skip-long-)` in class `[FilterReader](../../java/io/FilterReader.html "class in java.io")`  
    Parameters:  
    `n` \- The number of characters to skip  
    Returns:  
    The number of characters actually skipped  
    Throws:  
    `[IllegalArgumentException](../../java/lang/IllegalArgumentException.html "class in java.lang")` \- If `n` is negative.  
    `[IOException](../../java/io/IOException.html "class in java.io")` \- If an I/O error occurs

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