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Re: Comparing some of the ways to create objects

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Stefan Ram wrote:
> Scott Sauyet wrote:

>> But the privacy offered by these techniques, even without a keyword is
>> actually much stronger than that offered by Java or C# (I don't know
>> about C++.)  In those languages, you can use reflection to to still get
>> at the field.  In Javascript closure-based privacy, it's really hidden.
> 
> Java programs can be run with a security manager, and IIRC there is a
> »suppressAccessChecks« permission that can be denied to deny access to
> private fields via reflection.
> (I am not sure about this, I haven't tested it today.)

I'm more than six years out from regularly working with Java, so I may be 
a little rusty.  But I believe that field is precisely the reverse: a 
tool to _allow_ otherwise restricted code from viewing private or 
protected members.  That's certainly how the Javadocs seem to read.  [1]


> But the privacy of OOP is not meant to be a shield against malicious
> attacs, it is meant to be a means to help programmers not to access a
> private field inadvertently.

I've always thought of it a bit differently.  I picture it as a way to 
encapsulate internal state so that one can freely change implementation 
without the threat of breaking dependent code.  The shenanigans allowed 
by the combination of Reflection and ClassLoaders means there is little 
protection from malicious code running in the same VM, as far as I can 
see.  But the protection offered by encapsulation is real and very 
important.

 
> And one /can/ generate closures in Java too. In the Java program
> below, each of »e« and »e1« have their /own/ »closure variable«
> »a[ 0 ]« (which is not a field of a class).
> 
> [ ... details and code samples elided ... ]

Yes, I was gone from Java before version 8 was released, so I haven't 
really played around with this all that much.  But it's interesting 
because you answered a question a colleague and I were speculating about 
a few days ago, but weren't quite motivated enough to actually research.  
( :-> )  We knew that Java closures used static references; so you 
couldn't update a counter variable stored in a closure.  As I pointed 
that out as a somewhat-crippling handicap to one colleague, another 
speculated, "I wonder if you could use a container like an array and 
simply mutate the value stored inside."  Thank you for clearing that up 
for us!  :-)

So are those closure-based values as hidden as ones in Javascript?  That 
is, are they much more private than class members with the `private` 
keyword, which can still be accessed through reflection?  That would be 
interesting to know.  It doesn't change how the `private` and `protected` 
keywords work, but it would be interesting to know.


  [1]: <http://docs.oracle.com/javase/7/docs/api/java/lang/reflect/
ReflectPermission.html>

  -- Scott

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Comparing some of the ways to create objects John Harris <niam@jghnorth.org.uk.invalid> - 2016-04-03 16:09 +0100
  Re: Comparing some of the ways to create objects Scott Sauyet <scott@sauyet.com> - 2016-04-04 04:15 +0000
    Re: Comparing some of the ways to create objects Stefan Weiss <krewecherl@gmail.com> - 2016-04-04 15:20 +0200
      Re: Comparing some of the ways to create objects Scott Sauyet <scott@sauyet.com> - 2016-04-05 04:04 +0000
    Re: Comparing some of the ways to create objects John Harris <niam@jghnorth.org.uk.invalid> - 2016-04-04 16:48 +0100
      Re: Comparing some of the ways to create objects Scott Sauyet <scott@sauyet.com> - 2016-04-05 04:04 +0000
        Re: Comparing some of the ways to create objects John Harris <niam@jghnorth.org.uk.invalid> - 2016-04-07 15:07 +0100
          Re: Comparing some of the ways to create objects Scott Sauyet <scott@sauyet.com> - 2016-04-08 01:10 +0000
            Re: Comparing some of the ways to create objects John Harris <niam@jghnorth.org.uk.invalid> - 2016-04-08 14:55 +0100
    Re: Comparing some of the ways to create objects Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-04-04 22:12 +0200
      Re: Comparing some of the ways to create objects John Harris <niam@jghnorth.org.uk.invalid> - 2016-04-05 09:57 +0100
    Re: Comparing some of the ways to create objects John Harris <niam@jghnorth.org.uk.invalid> - 2016-04-06 16:41 +0100
      Re: Comparing some of the ways to create objects Scott Sauyet <scott@sauyet.com> - 2016-04-06 23:42 +0000
        Re: Comparing some of the ways to create objects John Harris <niam@jghnorth.org.uk.invalid> - 2016-04-07 16:09 +0100
          Re: Comparing some of the ways to create objects Scott Sauyet <scott@sauyet.com> - 2016-04-08 02:05 +0000
            Re: Comparing some of the ways to create objects John Harris <niam@jghnorth.org.uk.invalid> - 2016-04-08 15:43 +0100
              Re: Comparing some of the ways to create objects Scott Sauyet <scott@sauyet.com> - 2016-04-09 00:01 +0000
                Re: Comparing some of the ways to create objects Scott Sauyet <scott@sauyet.com> - 2016-04-09 16:46 +0000
                Re: Comparing some of the ways to create objects Scott Sauyet <scott@sauyet.com> - 2016-04-10 16:51 +0000
                Re: Comparing some of the ways to create objects Stanimir Stamenkov <s7an10@netscape.net> - 2016-05-08 17:27 +0300
                Re: Comparing some of the ways to create objects John Harris <niam@jghnorth.org.uk.invalid> - 2016-04-10 11:31 +0100
                Re: Comparing some of the ways to create objects John Harris <niam@jghnorth.org.uk.invalid> - 2016-04-10 11:52 +0100

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