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Groups > comp.lang.java.programmer > #34473
| From | Eric Sosman <esosman@comcast-dot-net.invalid> |
|---|---|
| Newsgroups | comp.lang.java.programmer |
| Subject | Re: Are you sure, Mr. Gosling? |
| Date | 2016-06-04 16:43 -0400 |
| Organization | A noiseless patient Spider |
| Message-ID | <nivehs$9e0$1@dont-email.me> (permalink) |
| References | <Gosling-20160604185910@ram.dialup.fu-berlin.de> <niva2t$13sk$1@gioia.aioe.org> |
On 6/4/2016 3:27 PM, Arne Vajhøj wrote:
> On 6/4/2016 2:01 PM, Stefan Ram wrote:
>> There is this famous book »The Java Programming Language,
>> Fourth Edition« by James Gosling et al.
>>
>> In it, it is written about the »idiom of copy constructor«:
>>
>> »This idiom is not used much within the Java class
>> libraries, because the preferred way to make a direct
>> copy of an object is by using the clone method.«
>>
>> Are you sure about this, Mr. Gosling?
Why ask here? Do you think he reads this newsgroup?
> I do not remember ever to have written a class with a constructor
> with a single argument of same type.
I've done it, but not very often. Usually it's when the class is
mutable (for what seem to be good reasons) but I need an instance that
won't be mutated:
class MyClass {
private final List<Thing> things = new ArrayList<>();
public void rememberThing(Thing thing) {
// Don't let the Thing change after I've remembered it.
things.add(new Thing(thing));
}
public Thing getThingAtIndex(int index) {
// Don't expose a remembered Thing to possible change.
return new Thing(things.get(index));
}
...
}
> And the only example that I can remember having seen
> is java.lang.String. And usage of that is usually a code
> smell.
Well, the JavaDoc suggests that any class implementing Collection
ought to provide a constructor that takes a Collection argument. So
we could *almost* say that ArrayList has a constructor that takes a
(slightly disguised) ArrayList as its argument. Similar remarks apply
to Map.
FWIW, Joshua Bloch appears to disagree with Gosling et al. From
"Effective Java:"
Is all this complexity [of implementing Cloneable] really
necessary? Rarely. [...] <b>you are probably better off
providing some other means of object copying or simply not
providing the capability.</b> [emphasis his]
<b>A fine approach to object copying is to provide a <i>copy
constructor</i>. [...]</b> [emphasis and italics his]
The copy constructor approach and its static factory variant
have many advantages over Cloneable/clone [...]
So: Who ya gonna trust? The guy who thought unsigned integers
were "too complex" or the guy who invented collections?
--
esosman@comcast-dot-net.invalid
"Don't be afraid of work. Make work afraid of you." -- TLM
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Re: Are you sure, Mr. Gosling? Arne Vajhøj <arne@vajhoej.dk> - 2016-06-04 15:27 -0400
Re: Are you sure, Mr. Gosling? Eric Sosman <esosman@comcast-dot-net.invalid> - 2016-06-04 16:43 -0400
Re: Are you sure, Mr. Gosling? Arne Vajhøj <arne@vajhoej.dk> - 2016-06-04 18:44 -0400
Re: Are you sure, Mr. Gosling? Eric Sosman <esosman@comcast-dot-net.invalid> - 2016-06-05 08:05 -0400
Re: Are you sure, Mr. Gosling? Arne Vajhøj <arne@vajhoej.dk> - 2016-06-05 08:31 -0400
Re: Are you sure, Mr. Gosling? Eric Douglas <e.d.programmer@gmail.com> - 2016-06-06 05:22 -0700
Re: Are you sure, Mr. Gosling? Eric Sosman <esosman@comcast-dot-net.invalid> - 2016-06-06 09:00 -0400
Re: Are you sure, Mr. Gosling? v_borchert@despammed.com (Volker Borchert) - 2016-06-06 16:06 +0000
Re: Are you sure, Mr. Gosling? Robert Klemme <shortcutter@googlemail.com> - 2016-06-06 22:56 +0200
Re: Are you sure, Mr. Gosling? Eric Douglas <e.d.programmer@gmail.com> - 2016-06-07 05:08 -0700
Re: Are you sure, Mr. Gosling? Eric Sosman <esosman@comcast-dot-net.invalid> - 2016-06-07 08:41 -0400
Re: Are you sure, Mr. Gosling? Martin Gregorie <martin@address-in-sig.invalid> - 2016-06-07 13:14 +0000
Re: Are you sure, Mr. Gosling? Eric Douglas <e.d.programmer@gmail.com> - 2016-06-07 06:30 -0700
Re: Are you sure, Mr. Gosling? Robert Klemme <shortcutter@googlemail.com> - 2016-06-07 19:10 +0200
Re: Are you sure, Mr. Gosling? Eric Douglas <e.d.programmer@gmail.com> - 2016-06-07 10:22 -0700
Re: Are you sure, Mr. Gosling? Mike Amling <mamling@chaff.us> - 2016-06-07 15:31 -0500
Re: Are you sure, Mr. Gosling? Eric Douglas <e.d.programmer@gmail.com> - 2016-06-08 06:31 -0700
Re: Are you sure, Mr. Gosling? Eric Sosman <esosman@comcast-dot-net.invalid> - 2016-06-08 10:41 -0400
Re: Are you sure, Mr. Gosling? Eric Douglas <e.d.programmer@gmail.com> - 2016-06-08 10:21 -0700
Re: Are you sure, Mr. Gosling? Eric Sosman <esosman@comcast-dot-net.invalid> - 2016-06-08 14:10 -0400
Re: Are you sure, Mr. Gosling? Robert Klemme <shortcutter@googlemail.com> - 2016-06-08 20:54 +0200
Re: Are you sure, Mr. Gosling? Eric Sosman <esosman@comcast-dot-net.invalid> - 2016-06-08 16:36 -0400
Re: Are you sure, Mr. Gosling? Robert Klemme <shortcutter@googlemail.com> - 2016-06-08 23:11 +0200
Re: Are you sure, Mr. Gosling? Lew <lewbloch@gmail.com> - 2016-06-10 12:20 -0700
Re: Are you sure, Mr. Gosling? Robert Klemme <shortcutter@googlemail.com> - 2016-06-14 19:10 +0200
Re: Are you sure, Mr. Gosling? Eric Sosman <esosman@comcast-dot-net.invalid> - 2016-06-07 17:12 -0400
Re: Are you sure, Mr. Gosling? Robert Klemme <shortcutter@googlemail.com> - 2016-06-07 23:25 +0200
Re: Are you sure, Mr. Gosling? Arne Vajhøj <arne@vajhoej.dk> - 2016-06-07 17:33 -0400
Re: Are you sure, Mr. Gosling? Arne Vajhøj <arne@vajhoej.dk> - 2016-06-06 21:18 -0400
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