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Re: Object constructors/destructors [message #185134 is a reply to message #185129] Fri, 28 February 2014 13:52 Go to previous messageGo to previous message
Christoph Michael Bec is currently offline  Christoph Michael Bec
Messages: 207
Registered: June 2013
Karma:
Senior Member
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.

--
Christoph M. Becker

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