Module java.base
Package 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

  • Field Summary

    Fields declared in class java.io.FilterReader

    in

    Fields declared in class java.io.Reader

    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

    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 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

    • 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
      IndexOutOfBoundsException - If off is negative, or len is negative, or len is greater than cbuf.length - off

    • 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

    • 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