PushbackInputStream class provides a pushback buffer so a program can
"unread" bytes onto the stream. These may be bytes the program has read from the stream or they may be bytes that come from somewhere else. The next time data is read from the stream, the "unread" bytes are read.
public void unread(int b) throws IOException public void unread(byte data, int offset, int length) throws IOException public void unread(byte data) throws IOException
By default the buffer is only one byte long, and trying to unread more than that throws an
However you can change the default buffer size with the second constructor:
public PushbackInputStream(InputStream in) public PushbackInputStream(InputStream in, int size)