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Thread: Converting Object to Long

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    Default Converting Object to Long

    How can I convert an Object to a Long?

    I have a method that returns an ArrayList of either Integer Objects or Long Objects, so it returns just an ArrayList of Objects. I need to convert those Objects to Longs so I can use them. I've tried parsing and casting, but both cause compiler errors.


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    Super Moderator helloworld922's Avatar
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    Default Re: Converting Object to Long

    Could you post your code? It's kind of hard to figure out what's going on without it.

    Does the ArrayList hold longs and integers at the same time, or is it either all longs or all integers?

    It sounds like reflection or wild-cards could help you solve this problem (or even just refactoring your code)

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    Super Moderator Norm's Avatar
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    Default Re: Converting Object to Long

    Or use instanceof before casting.

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    Default Re: Converting Object to Long

    The method returned either an ArrayList<Integer> or an ArrayList<Long>, depending on what was given to it. So since it could return either, it returned ArrayList<Object>. I needed to cast those Objects, regardless of Integer or Long as Longs. I figured out I could do this by saying:
    Long.parseLong(arr.get(y).toString());

    I was being stupid and tried to send the Long.parseLong method the object. After looking at the API, I realized I just had to toString it...

    I'm good now.

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    Super Moderator helloworld922's Avatar
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    Default Re: Converting Object to Long

    Rather than saying it returns a ArrayList of objects, use the wild generic qualifier.

    public ArrayList<?> myMethod()
    {
        // for ArrayList of longs:
        return new ArrayList<Long>();
        // for ArrayList of int's:
        return new ArrayList<Integer>();
    }

    Better yet, you can give it qualifiers for what it is going to return via polymorphism

    public ArrayList<? extends Number> theMethod()
    {
        // code. Return statements are the same as above
    }

    This allows you to actually return an ArrayList<Long> rather than an ArrayList<Object>.
    Last edited by helloworld922; August 19th, 2010 at 10:53 PM.

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    Default Re: Converting Object to Long

    I like that way. I'll have to use that in the future.

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