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NNTP-Posting-Date: Wed, 08 Jun 2011 11:33:36 -0500
Date: Wed, 08 Jun 2011 09:33:35 -0700
From: Patricia Shanahan <pats@acm.org>
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Subject: Re: What's the difference between and instance and an object?
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On 6/8/2011 8:54 AM, Abu Yahya wrote:
> On 6/8/2011 9:21 PM, Abu Yahya wrote:
>> On 6/6/2011 10:24 PM, Mayeul wrote:
>>> In other words, it cannot possibly build an instance of any other class,
>>> neither Object nor anything.
>>
>> Won't 'A' be an instanceOf Object?
>
> Err...I mean instanceof, with a lower-case 'o'.

There are two slightly different meanings of "X is an instance of Y".

1. X is an object whose class is Y. That is the meaning in which a
constructor can only return an instance of its own class. The expression
(new MyClass()), if it completes without exception or error, is always
an object whose class is MyClass.

2. X is an object whose class implements or extends Y. This is the
meaning that is tested by the "instanceof" operator. The expression

(x instanceof Y)

is true if x references an object whose class implements or extends Y.

(x instanceof Object) is true unless x is null.

Patricia