Supermarket operation support system - Software Development Case Studies in Java - page 386

public synchronized long startTransaction( long customer,
long employee)
throws Exception {
Connection conn # DriverManager.getConnection
(connection);
Statement stmt # conn.createStatement();
ResultSet rs # stmt.executeQuery(
"SELECT MAX(ID) AS M FROM TRANS");
long code;
if (rs.next())
code # rs.getLong("M") ! 1;
else
code # 1;
stmt.executeUpdate("INSERT INTO TRANS " !
"(ID,employee,customer,is_open)"
! " VALUES ( " ! code ! ", "
! employee ! "," !
customer ! ", 1)");
return code;
}
public void closeTransaction( long code)
throws Exception {
Connection conn # DriverManager
.getConnection(connection);
Statement stmt # conn.createStatement();
ResultSet rs # stmt.executeQuery(
"SELECT * FROM TRANS WHERE ID # " ! code);
Transaction trans # null ;
if (rs.next()) trans # new Transaction(rs);
if (trans ## null ) throw new Exception(
"Transaction non existent");
if (!trans.open) throw new Exception(
"Transaction is closed");
stmt.executeUpdate("UPDATE TRANS SET is_open # 0 " !
"WHERE ID # " ! code);
}
public synchronized void buy( long code, long quantity,
long transaction)
throws Exception {
Connection conn # DriverManager
.getConnection(connection);
Statement stmt # conn.createStatement();
ResultSet rs;
Transaction t;
try {
rs # stmt.executeQuery("SELECT * FROM TRANS WHERE ID # "
! transaction);