how to implement association relationship in Java

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newsnet customer - 04 Nov 2006 03:42 GMT

Hi,

I want to implement as association relationship in Java. I understand the implementation for this kind of relationship is called "containment". However, I can not find the code for this on the internet. From what is explained on the internet, I believe the code would look something like this:

/*A Car 'has a' Wheel relationship*/

public class wheel{
public wheel(){
}
}

public class Car{
Wheel w;

public Car(){
w = new Wheel();
}
}

Is this the basic idea?
by the way, what does containment mean?

ST

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hiwa - 04 Nov 2006 06:27 GMT

> what does containment mean?

Container Car contains Wheel.
Also you could use
Hashtable<Car,Wheel>
or
HashMap<Car,Wheel>
for representing association relationship.

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JanTheKing - 04 Nov 2006 15:49 GMT

Try an UML tool called JUDE (free) wherein you can create a simple
class diagram to depict association relationship (fairly simple). Then
click on "export to Java" to create the class files. That should
clarify the concept.

Cheers,
Jan

> > what does containment mean?Container Car contains Wheel.
> Also you could use
> Hashtable<Car,Wheel>
> or
> HashMap<Car,Wheel>
> for representing association relationship.

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LaieTechie - 08 Nov 2006 09:05 GMT

> Hi,
>
[quoted text clipped - 23 lines]
>
> ST

There are two types of relationships you should concern yourself with in
Java:

Has A: this indicates containment. In you example, a Car has a Wheel.
Your container class should have a member property ("instance variable")
of that type.

Is A: this denotes inheritance. A Car is a vehicle. You indicate
inheritance with "extends" (for classes) or "implements" (for interfaces).

Public class Car extends Vehicle {}

You may also run into "uses" relationships, which may translate into
instance variables or local variables (variables defined within a certain
scope, like a method).

HTH,
La`ie Techie

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Codedigestion - 09 Nov 2006 11:56 GMT

Peace,

I would like some help. As far as I've understood thus far:

a "is a" b = inheritance of 'a' from super('b')
a "has a" b = 'b' is a property of class 'a'

now how can I understand the relationship of an interface to a class,
as in:

'a' implements 'b'

Thanks in advance,
God Bless,

shree

> > Hi,
> >
[quoted text clipped - 42 lines]
> HTH,
> La`ie Techie

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Chris Uppal - 09 Nov 2006 13:24 GMT

> a "is a" b = inheritance of 'a' from super('b')
> a "has a" b = 'b' is a property of class 'a'
[quoted text clipped - 3 lines]
>
> 'a' implements 'b'

Unless you want to be pedantic, it's essentially the same as the 'is a' for
class/subclass relationship. It tells you that an 'a' is acceptable wherever a
'b' has been asked for.

Still speaking a bit sloppily; the 'is-a' relationship should really be
understood as 'can-be-used-as-if-it-were-a'. E.g: any Mammal can be used as if
it were an Animal. Now with interfaces, what the interface does is specify
what is /needed/ in order to be used as a <something>, so everything which
implements that interface can be used as if it were a <something>.

This could all be made more precise, but it would lead into a discussion of
what wrong with (or at best misleading about) Java's class-based type system,
and I don't think that would help at all just now.

-- chris

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how to implement association relationship in Java

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