question: public boolean fill ( Reader reader , int pos ) throws IOException { int res = reader . read ( fBuf ) ; if ( res == - 1 ) { fOffset = pos ; fLength = 0 ; return true ; } int charsRead = res ; while ( charsRead < BUFFER_SIZE ) { res = reader . read ( fBuf , charsRead , BUFFER_SIZE - charsRead ) ; if ( res == - 1 ) { fOffset = pos ; fLength = charsRead ; return true ; } charsRead += res ; } fOffset = pos ; fLength = BUFFER_SIZE ; return false ; }
target:  Fills the buffer by reading from the given reader.