Aggregation

Aggregation

1. Composition

   • each instance has the only reference to its contained object
   • container owns the object and it's not ok if the outside word wants to make changes
   • every time we want the object in or out the container we have to make defensive copies

2. Inheritance

   • It s a special kind of composition with a parent class and a child class
   • the child class inherits all the public feauture(methods and fields) of the parent class
   • when we want to access the parent feautres we use super and if we want to acces its constructor we use super()
   • another benefir of inheritance is polymorphysm: the child can be casted as a parent but still use the child method
   • the child can override the parent method
   • the child extends the parent class

3. container keeps a reference but its ok if changes happen in the outside world

4. while copying we just have to make sure the reference is the same