Groups > comp.lang.java.programmer > #36112

Re: I don't understand why the following doesn't call Rectangle

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From	Eric Sosman <esosman@comcast-dot-net.invalid>
Newsgroups	comp.lang.java.programmer
Subject	Re: I don't understand why the following doesn't call Rectangle
Date	Tue, 13 Dec 2016 11:42:52 -0500
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On 12/13/2016 10:42 AM, cdalten@gmail.com wrote:
> In the following lines of code....
>
>
> public class ComparableRectangle extends Rectangle
>     implements Comparable<ComparableRectangle> {
>   /** Construct a ComparableRectangle with specified properties */
>   public ComparableRectangle(double width, double height) {
>     super(width, height);
>   }
>[...]
>
> The author calls super() to construct a ComparableRectangle. How is this possible? Wouldn't super () invoke the Rectangle constructor, and thus construct a Rectangle?

     Yes!

     Keep in mind that a ComparableRectangle *is* a Rectangle -- a
specialized kind of Rectangle, but a Rectangle nonetheless.  Since
it is a Rectangle, it has a "Rectangle aspect" or "Rectangle-ness"
that needs to be initialized.  What piece of Java code initializes
the Rectangle-nature of things that are Rectangles?  The Rectangle
constructor, of course.

     Furthermore, a Rectangle *is* an Object, so the first thing
the Rectangle constructor does is invoke the Object constructor to
set up its Object-ness.  An Object *isn't* anything more general,
so the Object constructor needn't invoke anything further up the
line: It just initializes the Object-nature and returns to the
Rectangle constructor.  Which, in turn, initializes the Rectangle-
ness and returns to the ComparableRectangle constructor.  Which
has nothing more to do (in this case), so it just returns, having
arranged to set up the ComparableRectangle-ness, the Rectangle-ness,
and the Object-ness of the new instance.

     The ComparableRectangle constructor sets up a ComparableRectangle,
which is also a Rectangle, which is also an Object.  All three, at
the same time.

-- 
esosman@comcast-dot-net.invalid
"Nobody ever went broke underestimating the intelligence of the
American public." -- HLM (paraphrased)

Thread

I don't understand why the following doesn't call Rectangle cdalten@gmail.com - 2016-12-13 07:42 -0800
  Re: I don't understand why the following doesn't call Rectangle Eric Douglas <e.d.programmer@gmail.com> - 2016-12-13 07:52 -0800
    Re: I don't understand why the following doesn't call Rectangle cdalten@gmail.com - 2016-12-13 08:06 -0800
      Re: I don't understand why the following doesn't call Rectangle Eric Douglas <e.d.programmer@gmail.com> - 2016-12-13 08:20 -0800
  Re: I don't understand why the following doesn't call Rectangle Eric Sosman <esosman@comcast-dot-net.invalid> - 2016-12-13 11:42 -0500
  Re: I don't understand why the following doesn't call Rectangle lewbloch@gmail.com - 2016-12-13 12:47 -0800
    Re: I don't understand why the following doesn't call Rectangle Manuel Collado <m.collado@domain.invalid> - 2016-12-14 19:13 +0100

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