Association : An association is the relation between two objects. In other
words its connectivity between two objects. Aggregation and compositions are form
of association.
Aggregation: This is a part of a whole relationship where a part
can exist without a whole.
Aggregation is a weak association. Also called “has a” relationship.
Composition : This is a part of a whole relationship where a part
cannot exist without a whole. If a whole is deleted then all parts are deleted.
Composition is a Strong
association.
Example:
A House contains Room
and TV. Relationship between House and TV is aggregation and relation between
House and Room is composition.
A TV can exist without a
House-> Weak association (Aggregation)
A Room cannot exist without a House -> Strong association
(Composition).
Java Example :
Aggregation
Class LPG{
}
Class Car{
Car(LPG
objLPG) //Object is passed from outside
- weak relationship –LPG can exist without a car
{
}
}
Composition
Class Engine{}
Class Car{
Car(){
Engine
objEng = new Engine(); //lives within
car object - Strong relationship:
Engine cannot exist without car.
}
}
