Supermarket operation support system - Software Development Case Studies in Java - page 366

public String getName( long item) throws Exception {
assertConnected();
return server.getName(item);
}
public double getPrice( long item) throws Exception {
assertConnected();
return server.getPrice(item);
}
public String getCustomer( long code) throws Exception{
assertConnected();
String customerName # server.getCustomer(code);
if (customerName ## null ) return null ;
customer # code;
return customerName;
}
public void buy( long item, long quantity)
throws Exception{
assertConnected();
// if no transaction has been started, start a new one
if (transaction ## 0){
transaction # server.
startTransaction(customer,employee);
}
server.buy(item,quantity,transaction);
}
public void endTransaction() throws Exception {
assertConnected();
server.endTransaction(transaction);
transaction # 0;
}
}
The interface Market defines all the operations provided by the market
server. They are closely related to those available in the MarketProxy interface.
package Market;
public interface Market {
// authenticate an employee,
// return null in case of failure
public String authenticate( long employee,
String password);
// return the name of a customer,
// null if it doesn't exist
public String getCustomer( long customer);
// return the name of an item,
// null if it doesn't exist
public String getName( long item);