Difference between Association and Aggregation in Java

Association

Association in terms of objects refers to "has a" relationship between two related objects. For example, a employee has a communication address.

class Employee {
   String name;
   Address communicationAddress;
}
class Address {
   String address;
}

Aggregation

Aggregation in terms of objects refers to "has a"+ relationship between two related objects. For example, a department has multiple employees. It refers to having a collection of child objects in parent class. For example:

class Department {
   String name;
   List<Employee> employees;
}
class Employee {
   String name;
}