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Thread: Need help with a interface concept

  1. #1
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    Default Need help with a interface concept

    Ok, I was reading some java when they drop this code on me.

    //As an example, here is a method for finding the largest object in a pair of objects, for any objects that are instantiated from a class that implements Relatable:

    public Object findLargest(Object object1, Object object2) {
    Relatable obj1 = (Relatable)object1;
    Relatable obj2 = (Relatable)object2;
    if ( (obj1).isLargerThan(obj2) > 0)
    return object1;
    else
    return object2;
    }

    I can answer everything about this code, but only one little thing. Why is there a parentheses around Relatable in this Relatable obj1 = (Relatable)object1;?


  2. #2
    Super Moderator Norm's Avatar
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    Default Re: Need help with a interface concept

    Why is there a parentheses around Relatable
    That's called casting. The compiler wants you to tell it what type of object you are working with just to be sure you know what you are doing.

    There is also a check made at execution time that ensures that the object is of the type it is cast to. Otherwise you get an exception:
    Object obj = "asdf";
    Integer aI = (Integer)obj;

    java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Integer
    Last edited by Norm; September 13th, 2011 at 02:18 PM.

  3. #3
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    Default Re: Need help with a interface concept

    Thanks your the best Norm. I hate to say this, but I will probably never come back to this site. Because, that was the only thing in java I could not figure out.
    Last edited by drakenlord; September 13th, 2011 at 02:31 PM.

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