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Re: Object constructors/destructors [message #185137 is a reply to message #185136] Fri, 28 February 2014 16:03 Go to previous messageGo to previous message
Jerry Stuckle is currently offline  Jerry Stuckle
Messages: 2598
Registered: September 2010
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Senior Member
On 2/28/2014 10:52 AM, Christoph Michael Becker wrote:
> Jerry Stuckle wrote:
>
>> On 2/28/2014 8:52 AM, Christoph Michael Becker wrote:
>>> Jerry Stuckle wrote:
>>>
>>>> On 2/27/2014 12:28 PM, Christoph Michael Becker wrote:
>>>> > Jerry Stuckle wrote:
>>>> >
>>>> >> On 2/26/2014 5:39 PM, Christoph Michael Becker wrote:
>>>> >>> Jerry Stuckle wrote:
>>>> >>>
>>>> >>>> No matter how you look at it, PHP's implementation violates OO
>>>> >>>> principles and works differently than any other OO language.
>>>> >>>
>>>> >>> You have claimed that often enough, but yet you have not brought any
>>>> >>> proof.
>>>> >>>
>>>> >>> E.g. what happens in Java if an object that implements the
>>>> >>> java.io.Serializable interface is given as argument to
>>>> >>> java.io.OutputStream.writeObject()? Is the destructor called?
>>>> >>>
>>>> >>
>>>> >> Yes, it is.
>>>> >
>>>> > I strongly doubt that. On one hand this would mean you can't use the
>>>> > object as soon as it has been written to the stream, and on the other
>>>> > hand there are no *destructors* in Java (finalize() is similar to a
>>>> > destructor, but it is not guaranteed that it will be called).
>>>> > Furthermore it depends on the garbage collector, when an object will be
>>>> > *destroyed*.
>>>> >
>>>> >> But when the new object is created, a constructor is
>>>> >> called. You cannot unserialize an object without a constructor being
>>>> >> called first.
>>>> >
>>>> > I doubt that, too. After all, java.io.ObjectInputStream.readObject()
>>>> > returns an object, which of course has to be *created* -- but
>>>> > there's no
>>>> > need to call its *constructor*.
>>>> >
>>>>
>>>> No, because the constructor is called automatically.
>>>
>>> Wrong, see below.
>>>
>>>> > However, I believe our dissent mainly stems from different use of
>>>> > terms.
>>>> > I am accustomed to understand constructor/destructor as user defined
>>>> > functions (which can be defined for custom initialization/finalization
>>>> > tasks), while this may not be the common definition.
>>>> >
>>>>
>>>> They may be user defined, or they may be defined by the system (as in
>>>> the absence of a user-defined constructor).
>>>>
>>>> > When you're talking about OO principles wrt. to
>>>> > construction/destruction, you're most likely referring to RAII,
>>>> > which is
>>>> > not necessarily a general OO principle, and might not be possible to be
>>>> > cleanly implemented in garbage collected languages generally (consider
>>>> > cyclic references).
>>>> >
>>>>
>>>> No, I am not referring to RAII. I am referring to basic OO principles.
>>>>
>>>> > Anyway, I somewhat consider this discussion as harping on about
>>>> > principles, and I still don't see that PHP lacks the really important
>>>> > concepts regarding object (de)serialization and cloning.
>>>> >
>>>>
>>>> Just that it doesn't follow OO principles - which has caused me problems
>>>> in the past.
>>>
>>> To shorten further discussion I have installed the JDK 7u51, and written
>>> the following classes:
>>>
>>> ---- Foo.java ----
>>> public class Foo implements java.io.Serializable {
>>> protected int bar;
>>> public Foo() {
>>> System.out.println("Constructor of Foo called");
>>> bar = 0;
>>> }
>>> public int getBar() {
>>> return bar;
>>> }
>>> public void setBar(int value) {
>>> bar = value;
>>> }
>>> }
>>>
>>> ---- Demo.java ----
>>> import java.io.*;
>>>
>>> public class Demo {
>>> public static void main(String[] args)
>>> throws IOException, ClassNotFoundException {
>>> Foo foo = new Foo();
>>> foo.setBar(42);
>>> FileOutputStream fileOut = new FileOutputStream("./ser");
>>> ObjectOutputStream out = new ObjectOutputStream(fileOut);
>>> out.writeObject(foo);
>>> out.close();
>>> fileOut.close();
>>> System.out.println("Serialized foo");
>>> System.out.print("bar = ");
>>> System.out.println(foo.getBar());
>>> foo = null;
>>> FileInputStream fileIn = new FileInputStream("./ser");
>>> ObjectInputStream in = new ObjectInputStream(fileIn);
>>> foo = (Foo) in.readObject();
>>> in.close();
>>> fileIn.close();
>>> System.out.println("Unserialized foo");
>>> System.out.print("bar = ");
>>> System.out.println(foo.getBar());
>>> }
>>> }
>>>
>>> To compare that with PHP's behavior, I've written the following script:
>>>
>>> ---- demo.php ----
>>> <?php
>>>
>>> class Foo
>>> {
>>> protected $bar;
>>> public function __construct() {
>>> echo "Constructor of Foo called\n";
>>> $this->bar = 0;
>>> }
>>> public function getBar() {
>>> return $this->bar;
>>> }
>>> public function setBar($value) {
>>> $this->bar = $value;
>>> }
>>> }
>>>
>>> $foo = new Foo();
>>> $foo->setBar(42);
>>> file_put_contents('./ser', serialize($foo));
>>> echo "Serialized foo\nbar = ", $foo->getBar(), "\n";
>>> $foo = null;
>>> $foo = unserialize(file_get_contents('./ser'));
>>> echo "Unserialized foo\nbar = ", $foo->getBar(), "\n";
>>>
>>> Running the java programm and the PHP script (PHP 5.4.19 cli) produces
>>> the following output:
>>>
>>> Constructor of Foo called
>>> Serialized foo
>>> bar = 42
>>> Unserialized foo
>>> bar = 42
>>>
>>> Any conclusions are left to the reader.
>>>
>>
>> Which shows just how little you understand programming.
>>
>> In either case you have not created a new Foo object before serializing;
>> you have only serialized into an existing object. So obviously no
>> constructor is called.
>
> Of course, I have created a new Foo object before serializing in both
> cases. You're probably talking about the unserializing code (please
> look up the difference), but in this case your statement is wrong, as I
> have assigned null to $foo (what would not have been necessary, though).
>
> However, maybe you want
>
> $foo = null;
>
> replaced by
>
> $foo = new Foo();
>
> (resp. for the Java code). While the only benefit of this change would
> be to keep the processor busy, it does no real harm (unless in a not
> garbage collected environment, where it would create a memory leak).
>
> So what do you think (or rather guess), the last line of the output
> would be when changing the code repectively? Answer: bar = 42. That
> proofs that the constructor is not called on the unserialized object.
>
> Anyway, both programs behave equivalent, so Java also does not follow
> basic OO principles wrt. to object (un)serialization, according to your
> claim. However, you have stated it would, so obviously there's a
> contradiction.
>
>> Your stoopidity is amazing.
>
> You may consider changing your attitude to not make a fool of you in the
> public, again.
>

Yes, you continue to make a fool of yourself in public - as your last
statement shows. You have absolutely NO idea what you are talking
about, or how OO works.

I correspond off-list with some knowledgeable people who have followed
this conversation. They can't believe I even try to educate you. It's
like teaching a pig to sing.

And I'm through wasting my time. Your comments aren't even worth a
response (which is why I also refused to fall into your trap as to how I
define an "expression").

You don't discuss. You argue for the sake of argument.

--
==================
Remove the "x" from my email address
Jerry Stuckle
jstucklex(at)attglobal(dot)net
==================

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