There are mainly two types of relationships between classes in JAVA

• Inheritance (IS-A)

• Association (HAS-A)

Inheritance

In inheritance, the child class object carries the body of the parent class when initiated. This is achieved using the "extends" keyword.

class Vehicle
{

}
class car extends Vehicle
{

}

Association

Association is the relation between two separate classes established through objects. There are two forms of association

• Aggregation

• Composition

In Aggregation, both entries can survive individually, which means ending one entity will not affect the other.

For example, consider a car having a music player and an engine. The music player can work even without a car; this indicates aggregation, whereas an engine cannot work without a car this is an example of composition.

class Vehicle
{

}
class car 
{
    Engine e=new Engine();
}

Advantages

• Code reusability

• Cost cutting

• Reduce redundancy