CODEWITHSUNDEEP
javaoop
St.Antario
St.Antario

Reputation: 27375

Is it association or aggregation?

I'm trying to understand object oriented approach by the following simple example:

I have the class:

public class TotalRestiction{

    private Restriction r;

    public add(RestictionItem i){
        //updating the Restriction field
        //depends on the RestrictionItem
    }

    private static class Restriction{
        //...
    }

    public Collection<Object> getObjects(){
        //...
    }
}

public interface RestrictionItem{

    //...
}

It's not clear to me what is the exact relationship between those classes. Is it aggregation or association? I tend to say that it's aggregation, because the TotalRestriction aggregates the RestrictionItems, encapsulated within the Restriction static nested class. But I'm not pretty sure about that.

Upvotes: 2

Views: 77

Answers (2)

VIjay J
VIjay J

Reputation: 766

If you are instantiating class TotalRestriction as:

TotalRestriction tr=new TotalRestriction(new Restriction());

and in TotalRestriction class constructor is as :

   class TotalRestriction{
      Restriction r;
      public TotalRestriction(Restriction r){
         this.r=r;
      }
   }

then it is Aggregation

if you are using like this:

class TotalRestriction{
      Restriction r;
      public TotalRestriction(){
         r=new Restriction();
      }
   }

then it is Association because class TotalRestriction uses service of class Restriction .

Upvotes: 0

eis
eis

Reputation: 53462

Association would be when it would use another class, which does not have to be encapsulated. Composition would be when your class has a has-a relationship with those classes, e.g. TotalRestriction has-a RestrictionItems. With Aggregation the class also has a has-a relationship, but the other classes also exist independently of the parent class, which is not the case with Composition..

In your case, I'd say Restriction class has a aggregation relationship towards RestrictionItem, and TotalRestriction has a composition relationship towards Restriction.

Upvotes: 1

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