From lliao@ren.eecis.udel.edu Sun Nov 17 21:55:52 2002
Date: Sun, 17 Nov 2002 21:55:22 -0500 (EST)
From: Li Liao <lliao@ren.eecis.udel.edu>
Subject: Re: testing equality



> Should we test equality for Numbers only or should we do it for Objects
> as well? (case 3)

Both numbers and objects.

> If we have to do it for objects, then I assume that two objects are
> equal if their names are the same and they are objects of
> the same class. Is that correct?

Two expressions are equal when they evaluate to the same object.
As each object is assigned a unique id at creation, two objects
are the same if they have the same id.

The null expression receives special treatment. It has the special null
type, which--for the purposes of typechecking--is considered to be a
subtype of every object type. In other words, the null expression can be
used anywhere an expression with an object type is expected except on the
left-hand side of a field/method access or the right-hand side of a
downcast.

While null has no id, it is considered as object.
Therefore, when two expressions are evaluated
to "VNull", these two expressions are said to be equal.

I hope this is helpful.

Li