An association class represents additional information about an association. It is a normal class but plays a special role from a design point of view.
A Man class and a Woman class are linked with a ‘married to’ association and there is a need to store the date of marriage. However, that data is related to the association rather than specifically owned by either the Man object or the Woman object. In such situations, an additional association class can be introduced, e.g. a Marriage class, to store such information.
Implementing association classes
There is no special way to implement an association class. It can be implemented as a normal class that has variables to represent the endpoint of the association it represents.
In the code below, the Transaction class is an association class that represents a transaction between a Person who is the seller and another Person who is the buyer.
class Transaction {
//all fields are compulsory
Person seller;
Person buyer;
Date date;
String receiptNumber;
Transaction(Person seller, Person buyer, Date date, String receiptNumber) {
//set fields
}
}