public String toString() {
	//send ANSI code "ESC[0;0H" to place cursor in upper left
	//String retStr = "[0;0H";
	//emacs shortcut: C-q, then press ESC
	//emacs shortcut: M-x quoted-insert, then press ESC
	String retStr = "";
	int i, j;
	for( i=0; i<h; i++ ) {
	    for( j=0; j<w; j++ )
		if (maze[i][j] == null)
		    retStr+= " ";
		else
		    retStr = retStr + maze[i][j];
	    retStr = retStr + "\n";
	}
	return retStr;
    }