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Thread: How to use Generics (1 generic anyway)

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    Smile How to use Generics (1 generic anyway)

    Generic classes like

    Vector<> , ArrayLIst<>, Set<> , HashSet<>, Collection<>, LinkedList<>, TreeSet<>, and Tree<>

    all are generic. (Ones like Map<><>, HashMap<><> , and TreeMap<><> I don't know much about other than that they use tables like Hash Tables, which I really don't know much about yet. Sorry.)

    These store Object and its subclasses. They don't store primitives but do store

    Integer, Character, Double, Float, Long, Short, Byte, Boolean, String, and other types like that.

    Unlike arrays, these guys can be expanded or decreased in size.

    Kind of like arrays, these classes can also store other Generic, or even of the same type, inside of them.

    ArrayLists, LinkedLists, and Vectors have methods to get the data at them at a specific index.

    Like arrays, data for all these Generics start with index 0.

    Classes like Set and HashSet and TreeSet don't have a way of directly accessing the data in them, except maybe printing out all the data in a toString(). However, using an Iterator, you may be able to do this somehow...though I'm not fully sure how exactly as I haven't used them much myself.

    TreeSets and Trees like binary search trees require the generic parameter (Usually I've use a T) to implement comparable.

    This is done using

    ClassName<T extends Comparable>

    For some reason you have to use extends for both extending an implementing.

    Also,

    ClassName<T> extends Comparable is the class in general, not the parameter being made to have to implement Comparable..

    You can extend more than one as long as only 1 at most is a class.

    There's also the notoation

    <?T?> but I don't know much about that.

    These generics in general are usually set up in some format like this

    GenericClass<ClassName> gc = new GenericClass<ClassName>(params);


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    Super Moderator helloworld922's Avatar
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    Default Re: How to use Generics (1 generic anyway)

    Is there a question associated with this?

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    Default Re: How to use Generics (1 generic anyway)

    Quote Originally Posted by helloworld922 View Post
    Is there a question associated with this?
    My thoughts exactly. I would hope this isn't supposed to be some sort of how to...because not only is it difficult to follow, but some of this information is incorrect.

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    Default Re: How to use Generics (1 generic anyway)

    What does the <?T?> do?

    It was originally going to be a how to(What's incorrect? If I was wrong anywhere...I'd like to know.)

    Sets don't have a get() method.

    1.) How would you get the stuff at each index then?

    2.) What are double Generics used for and how do they work?

    3.) What info was incorrect? (Maybe the stuff about Sets...but by directly access...I meant something like a get method, i.e., not having to use an Iterator...whatever that is. Learned a bit about it but can't really recall much.

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    Super Moderator copeg's Avatar
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    Default Re: How to use Generics (1 generic anyway)

    It was originally going to be a how to(What's incorrect? If I was wrong anywhere...I'd like to know.)
    Constructive criticism: a good how to will require much more than this. There isn't even any code demonstrations, a reasoning behind what generics actually accomplish, when they should be used, how to write classes which utilize the power of generics. I misread quite a bit of this post when I first read this (sorry, but it wasn't that hard to misread) and jumped to the gun that there were several mistakes (let be frank, you do have a tendency to provide incorrect advice). After going through it a bit more thoroughly I'd say its incorrect in calling it a how to and partially incorrect as the direct access of the contents of a Set - this could be debatable, but shows a slight mis-understanding on your part of what exactly a Set is.
    My suggestion: if you want to write a how to I suggest you follow the outline some of the fantastic ones that can be found in the code snippets and tutorials thread, know your subject, write clear and concise, and if you don't know what something is (case in point Iterator) then look it up. How to's should NOT contain lines like "you may be able to do this somehow...though I'm not fully sure how exactly"
    Last edited by copeg; February 7th, 2011 at 05:21 PM.

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