Class PushbackInputStream

Field Detail

• buf

  protected byte[] buf

  The pushback buffer.

  Since:

  JDK1.1

• pos

  protected int pos

  The position within the pushback buffer from which the next byte will be read. When the buffer is empty, pos is equal to buf.length; when the buffer is full, pos is equal to zero.

  Since:

  JDK1.1

Constructor Detail

• PushbackInputStream

  public PushbackInputStream(InputStream in,
                     int size)

  Creates a PushbackInputStream with a pushback buffer of the specified size, and saves its argument, the input stream in, for later use. Initially, there is no pushed-back byte (the field pushBack is initialized to -1).

  Parameters:

  in - the input stream from which bytes will be read.

  size - the size of the pushback buffer.

  Throws:

  IllegalArgumentException - if size is <= 0

  Since:

  JDK1.1

• PushbackInputStream

  public PushbackInputStream(InputStream in)

  Creates a PushbackInputStream and saves its argument, the input stream in, for later use. Initially, there is no pushed-back byte (the field pushBack is initialized to -1).

  Parameters:

  in - the input stream from which bytes will be read.

Method Detail

• read

  public int read()
           throws IOException

  Reads the next byte of data from this input stream. The value byte is returned as an int in the range 0 to 255. If no byte is available because the end of the stream has been reached, the value -1 is returned. This method blocks until input data is available, the end of the stream is detected, or an exception is thrown.

  This method returns the most recently pushed-back byte, if there is one, and otherwise calls the read method of its underlying input stream and returns whatever value that method returns.

  Overrides:

  read in class FilterInputStream

  Returns:

  the next byte of data, or -1 if the end of the stream has been reached.

  Throws:

  IOException - if this input stream has been closed by invoking its close() method, or an I/O error occurs.

  See Also:

  InputStream.read()

• read

  public int read(byte[] b,
         int off,
         int len)
           throws IOException

  Reads up to len bytes of data from this input stream into an array of bytes. This method first reads any pushed-back bytes; after that, if fewer than len bytes have been read then it reads from the underlying input stream. If len is not zero, the method blocks until at least 1 byte of input is available; otherwise, no bytes are read and 0 is returned.

  Overrides:

  read in class FilterInputStream

  Parameters:

  b - the buffer into which the data is read.

  off - the start offset in the destination array b

  len - the maximum number of bytes read.

  Returns:

  the total number of bytes read into the buffer, or -1 if there is no more data because the end of the stream has been reached.

  Throws:

  NullPointerException - If b is null.

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

  IOException - if this input stream has been closed by invoking its close() method, or an I/O error occurs.

  See Also:

  InputStream.read(byte[], int, int)

• unread

  public void unread(int b)
              throws IOException

  Pushes back a byte by copying it to the front of the pushback buffer. After this method returns, the next byte to be read will have the value (byte)b.

  Parameters:

  b - the int value whose low-order byte is to be pushed back.

  Throws:

  IOException - If there is not enough room in the pushback buffer for the byte, or this input stream has been closed by invoking its close() method.

• unread

  public void unread(byte[] b,
            int off,
            int len)
              throws IOException

  Pushes back a portion of an array of bytes by copying it to the front of the pushback buffer. After this method returns, the next byte to be read will have the value b[off], the byte after that will have the value b[off+1], and so forth.

  Parameters:

  b - the byte array to push back.

  off - the start offset of the data.

  len - the number of bytes to push back.

  Throws:

  IOException - If there is not enough room in the pushback buffer for the specified number of bytes, or this input stream has been closed by invoking its close() method.

  Since:

  JDK1.1

• unread

  public void unread(byte[] b)
              throws IOException

  Pushes back an array of bytes by copying it to the front of the pushback buffer. After this method returns, the next byte to be read will have the value b[0], the byte after that will have the value b[1], and so forth.

  Parameters:

  b - the byte array to push back

  Throws:

  IOException - If there is not enough room in the pushback buffer for the specified number of bytes, or this input stream has been closed by invoking its close() method.

  Since:

  JDK1.1

• available

  public int available()
                throws IOException

  Returns an estimate of the number of bytes that can be read (or skipped over) from this input stream without blocking by the next invocation of a method for this input stream. The next invocation might be the same thread or another thread. A single read or skip of this many bytes will not block, but may read or skip fewer bytes.

  The method returns the sum of the number of bytes that have been pushed back and the value returned by available.

  Overrides:

  available in class FilterInputStream

  Returns:

  the number of bytes that can be read (or skipped over) from the input stream without blocking.

  Throws:

  IOException - if this input stream has been closed by invoking its close() method, or an I/O error occurs.

  See Also:

  FilterInputStream.in, InputStream.available()

• skip

  public long skip(long n)
            throws IOException

  Skips over and discards n bytes of data from this input stream. The skip method may, for a variety of reasons, end up skipping over some smaller number of bytes, possibly zero. If n is negative, no bytes are skipped.

  The skip method of PushbackInputStream first skips over the bytes in the pushback buffer, if any. It then calls the skip method of the underlying input stream if more bytes need to be skipped. The actual number of bytes skipped is returned.

  Overrides:

  skip in class FilterInputStream

  Parameters:

  n - the number of bytes to be skipped.

  Returns:

  the actual number of bytes skipped.

  Throws:

  IOException - if the stream does not support seek, or the stream has been closed by invoking its close() method, or an I/O error occurs.

  Since:

  1.2

  See Also:

  FilterInputStream.in, InputStream.skip(long n)

• markSupported

  public boolean markSupported()

  Tests if this input stream supports the mark and reset methods, which it does not.

  Overrides:

  markSupported in class FilterInputStream

  Returns:

  false, since this class does not support the mark and reset methods.

  See Also:

  InputStream.mark(int), InputStream.reset()

• mark

  public void mark(int readlimit)

  Marks the current position in this input stream.

  The mark method of PushbackInputStream does nothing.

  Overrides:

  mark in class FilterInputStream

  Parameters:

  readlimit - the maximum limit of bytes that can be read before the mark position becomes invalid.

  See Also:

  InputStream.reset()

• reset

  public void reset()
             throws IOException

  Repositions this stream to the position at the time the mark method was last called on this input stream.

  The method reset for class PushbackInputStream does nothing except throw an IOException.

  Overrides:

  reset in class FilterInputStream

  Throws:

  IOException - if this method is invoked.

  See Also:

  InputStream.mark(int), IOException

• close

  public void close()
             throws IOException

  Closes this input stream and releases any system resources associated with the stream. Once the stream has been closed, further read(), unread(), available(), reset(), or skip() invocations will throw an IOException. Closing a previously closed stream has no effect.

  Specified by:

  close in interface Closeable

  Specified by:

  close in interface AutoCloseable

  Overrides:

  close in class FilterInputStream

  Throws:

  IOException - if an I/O error occurs.

  See Also:

  FilterInputStream.in