PHP Basics: Classes and Objects (3) constructors and destructors _php techniques

Constructors
The PHP 5 allowable developer defines a method as a constructor in a class. Classes with constructors Call this method the first time you create an object, so it is ideal to do some initialization before using the object.
Attention:
If a constructor is defined in a subclass, it does not implicitly invoke the constructor of its parent class. To execute the constructor of the parent class, you need to call Parent::__construct () in the constructor of the subclass. (?? Obviously different from other languages??

Example 10.8. Using the new standard constructor
Class BaseClass {
function __construct () {
Print "in BaseClass constructor\n";
}
}

Class Subclass extends BaseClass {
function __construct () {
Parent::__construct ();
Print "in subclass constructor\n";
}
}
$obj = new BaseClass ();
$obj = new Subclass ();

For backward compatibility, if PHP 5 does not find the __construct () function in the class, it tries to look for a legacy constructor, which is a function with the same name as the class. So the only thing that will create a compatibility problem is that there is already a method named __construct () in the class, but it is not a constructor.

destructor
PHP 5 introduces the concept of destructors, which is similar to other object-oriented languages, such as C + +. Destructors are executed when all references to an object are deleted or when an object is explicitly destroyed.
Example 10.9. destructor examples
Class Mydestructableclass {
function __construct () {
Print "in constructor\n";
$this->name = "Mydestructableclass";
}

function __destruct () {
Print "destroying". $this->name. "\ n";
}
}
$obj = new Mydestructableclass ();
As with constructors, the destructor of a parent class is not invoked by the engine. To perform a destructor for a parent class, you must explicitly call Parent::__destruct () in the destructor body of the subclass. (?? Obviously different from other languages??
Attention:
The destructor is invoked when the script is closed, at which point all header information has been sent.
Attention:
Attempting to throw an exception in a destructor can result in a fatal error.