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Thread: Doubt regarding LIST

  1. #1
    Junior Member
    Join Date
    Feb 2010
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    Default Doubt regarding LIST

    Hi i have doubt regarding list .
    I have a List<Operator> type and a List<SQLExpr> type and I want to use them interchangeably like i want to add a List<SQLExpr> element to List<Operator> so i how can i do it ,explicitly casting in not working.So what should i do.

    Let me frame my question properly

    How to cast List<A> type element into List<B> type element

    somebody plz help


  2. #2
    Super Moderator helloworld922's Avatar
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    Jun 2009
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    Default Re: Doubt regarding LIST

    Unless one is a sub-class of the other, you can't cast (and even then, you can only cast up, exceptions being objects viewed as a poly-morphed super object). What you can do is declare your list to hold elements that both objects initially inherited from (this is the basis for polymorphism and OOP code re-use):

    public class A
    public class B extends A
    public class C extends A
    public class Main
         public static void main(String[] args)
              List<A> list = new ArrayList<A>();
              list.add(new B());
              list.add(new C());
              list.add(new A());

    If you don't want to create your own super class, you can use the Object class since everything inherits from Object.

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