Aggregation is a special form of association. It is also a relationship between two classes like association, however its a directional association, which means it is strictly a one way association. It represents a Has-A relationship.
Aggregation is a relationship between two classes that
is best described as a "has-a" and "whole/part" relationship.
example:
imagine a Student class that stores information about
individual students at a school. Now let's say there is a Subject class that
holds the details about a particular subject (e.g., maths,history, geography).
If the Student class is defined to contain a Subject object then it can be said
that the Student object has-a Subject object. The Subject object also makes up
part-of the Student object, after all there is no student without a subject to
study. The Student object is therefore the owner of the Subject object.
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public class Subject{ private String name; public void setName(String name) { this.name = name; } public String getName() { return name; } } public class Student { private Subject[] studyAreas = new Subject[10]; //the rest of the Student class }(); } } |