Creates a <code>PushbackInputStream</code>
with a pushback buffer of the specified <code>size</code>,
and saves its argument, the input stream
<code>inputStream</code>, for later use. Initially,
the pushback buffer is empty.
@param inputStream the input stream from which bytes will be read.
@param size the size of the pushback buffer.
@exception IllegalArgumentException if {@code size <= 0}
Creates a <code>PushbackInputStream</code> with a pushback buffer of the specified <code>size</code>, and saves its argument, the input stream <code>inputStream</code>, for later use. Initially, the pushback buffer is empty.
@param inputStream the input stream from which bytes will be read. @param size the size of the pushback buffer. @exception IllegalArgumentException if {@code size <= 0}