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  1. #1
    mattlindsay is offline Member
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    Default Best way to handle a collection of objects?

    Hi, Im pretty new to java although not new to programming in general.

    I wish to create an entity (for example, call it "BookClub"). That entity can have an unknown number of child objects (for example call them "Members").

    I want to have a collection that I can call methods on (for example "BookClub.sendMessage()"). In this way, I can write some code that will iterate through all members of the "BookClub" and send a message to each one of the "Member.GetEmailAddress()"

    Is the solution to use java collections to do this, or am I missing something very obvious about just using classes?!

    Hope that all makes sense!!

    Cheers, Matt

  2. #2
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    JosAH is offline Moderator
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    Quote Originally Posted by mattlindsay View Post
    Hi, Im pretty new to java although not new to programming in general.

    I wish to create an entity (for example, call it "BookClub"). That entity can have an unknown number of child objects (for example call them "Members").

    I want to have a collection that I can call methods on (for example "BookClub.sendMessage()"). In this way, I can write some code that will iterate through all members of the "BookClub" and send a message to each one of the "Member.GetEmailAddress()"

    Is the solution to use java collections to do this, or am I missing something very obvious about just using classes?!
    Forget all the Java technology for a moment and think OOP: for a class D to be able to extend a class B, a D is a B. In your case: is a Member a Bookclub? I don't think so, I think all Members together form a BookClub, so a Bookclub has a Member and that smells like composition, i.e. a BookClub has a collection of some sort, filled with Members. If you feel like it you can read about the gory details if you google for "Liskov Substitution Principle".

    kind regards,

    Jos
    The only person who got everything done by Friday was Robinson Crusoe.

  3. #3
    mattlindsay is offline Member
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    An excellent answer. You're quite right, it is composition.... I guess that leads me to the next part.... how do I implement it!! :S

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    Fubarable is offline Moderator
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    Quote Originally Posted by mattlindsay View Post
    An excellent answer. You're quite right, it is composition.... I guess that leads me to the next part.... how do I implement it!! :S
    Try it first. Your first guess will likely be pretty close.

  5. #5
    JosAH's Avatar
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    Quote Originally Posted by mattlindsay View Post
    An excellent answer. You're quite right, it is composition.... I guess that leads me to the next part.... how do I implement it!! :S
    It's quite simple: a BookClub looks like this:

    Java Code:
    public class BookClub {
       private Collection<Member> members= ...;
       ...
       public void addMember(Member member) { members.add(member); }
       ...
    }
    I don't know what methods you want to call on those members, but a BookClub object can call that method on each and every member in its members Collection.

    kind regards,

    Jos
    The only person who got everything done by Friday was Robinson Crusoe.

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