Aggregation

Aggregation means HAS –A relationship

Eg: Employee has Address

ie-

class Employee{

int id;

String name,salary;

Address address;//Address is a class

…

}

employee -> name, id, salary also has Address -> which itself has different attribute like pincode, city, country etc.

When there is no IS-A relationship(ie: inheritance), best way of code reuse is aggregation.

Inheritance should be used only if the –IS-A relationship is maintained in the life time of the object, otherwise aggregation is the best choice.