CODEWITHSUNDEEP
javac++oop
KKK
KKK

Reputation: 1662

How to write Composition and Aggregation in java

I want to know how to identify composition and aggregation code in java. I have C++ Code, But I don't understand how to write in java.

Composition

class A {};
class B { A composited_A; };

Aggregation via Pointer

class A {};
class B
{
A* pointer_to_A;
B(A anA){ 
pointer_to_A = &anA;
}

Can anyone please tell me how both are working in JAVA. (I know what is meant by Composition and aggregation ) };

Upvotes: 5

Views: 3457

Answers (3)

KKK
KKK

Reputation: 1662

I think this is best way to express Composition and Aggregation With Java Code.

Composition

public class Person  
{  
    private final Name name;  

    public Person (String fName, String lName)  
    {  
        name = new Name(fName, lName);  
    }  

    //...  
}

Aggregation

public class Person  
{  
    private Costume currentClothes;  

    public void setClothes(Costume clothes)  
    {  
        currentClothes = clothes;  
    }  

    //...  
}

Source

Upvotes: -1

Konrad Rudolph
Konrad Rudolph

Reputation: 546123

Java itself simply does not make the distinction between composition and aggregation. You cannot express the idea of ownership of a reference in the Java type system – if you explicitly need to express ownership you must denote this with some other means (usually simply by constructing a new object to be stored in the instance of a class).

Since Java has a GC, ownership for memory doesn’t need to be expressed at all; memory is owned and managed solely by the GC. Of course, the same is not true for other resources and here you might still want to express ownership.

Upvotes: 8

Russell Zahniser
Russell Zahniser

Reputation: 16364

In Java, objects are only referenced by pointers. This means that a field of type A is really a reference to an A object. It also means that that field will always start as a null pointer, and you must explicitly assign it to new A() or whatever.

Edit:

class B {
   A a;

   B(A a) {
      this.a = a;
   }

   B() {
      this(new A());
   }
}

Upvotes: 1

Related Questions