public String toString() {
	String retStr = "\n-----------------------------------------\n";
	retStr += "    ";
	for (int i = 1; i < 10; i ++) {
	    retStr += i + "   ";
	    if (i % 3 == 0) {
		retStr += " ";
	    }
	}

	for (int i = 0; i < 9; i++) {
	    if ( i % 3 == 0) {
		retStr += "\n  ---------------------------------------";
	    }
	    retStr += "\n" + converter(i) +  " ";
	    
	    for (int n = 0; n < 9; n++) {
		retStr += "|";
		if (_board[i][n] == 0) {
		    retStr += "   ";
		}
		else {
		    retStr += " " + _board[i][n] + " ";
		}
		if ( (n + 1) % 3 == 0) {
		    retStr += "|";
		}
	    }
	}
	retStr += "\n  ---------------------------------------";

	return retStr;
    }