Need help with a interface concept

**drakenlord** · September 13th, 2011, 02:02 PM

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;?

**Norm** · September 13th, 2011, 02:08 PM

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

**drakenlord** · September 13th, 2011, 02:17 PM

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.

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