+-------------------------------------------------------------------------------+
| = This is haohappy read < >
| = Notes in Classes and objects Chapter
| = Translation-based + personal experience
| = Please do not reprint in order to avoid the unnecessary trouble that may occur.
| = Welcome criticism, hope and all the PHP enthusiasts to progress together!
| = PHP5 Research Center: http://blog.csdn.net/haohappy2004
+-------------------------------------------------------------------------------+
*/
Section fourth-constructors and destructors
If you declare a function in a class named __construct, the function will be treated as a constructor and executed when an object instance is created. Clearly, __ is an underscore of two. Just like any other function, constructors may have parameters or default values. You can define a class to create an object and put its properties all in one statement (statement).
You can also define a function called __destruct, and PHP will call this function before the object is destroyed. It is called a destructor.
Inheritance is a powerful feature of a class. A class (subclass/derived class) can inherit the functionality of another class (parent/base class). The derived class will contain all the properties and methods of the base class, and other properties and methods can be added to the derived class. You can also override the base class's methods and properties. As shown in 3.1.2, you can use the extends keyword to inherit a class.
You might want to know how a constructor is inherited. When they are inherited along with other methods, they are not executed when the object is created.
If you need this feature, you need to use the following:: operator in chapter two. It allows you to point to a namespace. The parent points to the parental namespace, and you can use Parent::__construct to invoke the constructor of the parent class.
Some object-oriented languages name constructors after the class. This is true for the first few versions of PHP, which is still valid. That is, if you name a class animal and you create a name in it that is also animal, this method is the constructor. If a class has __ Construt constructor and the same function as the class name, PHP will treat __construct as a constructor. This makes the classes written in the previous PHP version still available. However, the new script (PHP5) should use __construct.
This new method of declaring constructors in PHP allows constructors to have a unique name, regardless of the name of the class in which it resides. When you change the name of a class, you do not need to change the name of the constructor.
You might give constructors a way to access the constructor in PHP just like any other class method. Access will affect the ability to instantiate objects from within a certain range. This allows the implementation of some fixed design patterns, such as the singleton mode.
destructor, as opposed to a constructor function. PHP calls them to destroy an object from memory. By default, PHP simply frees the memory occupied by the object's properties and destroys the object-related resources. Destructors allow you to execute arbitrary code after an object is used to clear memory.
When PHP decides that your script is no longer related to the object, the destructor is called. Within the namespace of a function, this occurs at the time of the function return. For global variables, this happens at the end of the script. If you want to explicitly destroy an object, you can assign any other value to the variable that points to the object. Variables are usually assigned on duty to null or called unset.
In the following example, the number of objects instantiated from a class is computed. The counter class adds value from the constructor, reducing the value in the destructor.
Once you have defined a class, you can use new to create an instance of the class. The definition of a class is a design diagram, and an instance is a component placed on an assembly line. New requires the name of the class and returns an instance of the class. If the constructor requires parameters, you should enter the parameters after new.
Copy CodeThe code is as follows: Class Counter
{
private static $count = 0;
function __construct ()
{
Self:: $count + +;
}
function __destruct ()
{
Self:: $count--;
}
function GetCount ()
{
Return self:: $count;
}
}
Establish the first instance
$c = new Counter ();
Output 1
Print ($c->getcount (). "
\ n ");
Create a second instance
$c 2 = new Counter ();
Output 2
Print ($c->getcount (). "
\ n ");
Destroying instances
$c 2 = NULL;
Output 1
Print ($c->getcount (). "
\ n ");
?>
When you create a new instance, the memory is prepared to store all the properties. Each instance has its own unique set of properties. However, the method is shared by all instances of the class.
http://www.bkjia.com/PHPjc/316955.html www.bkjia.com true http://www.bkjia.com/PHPjc/316955.html techarticle +-------------------------------------------------------------------------------+ |= This is haohappy read corephpprogramming |= in ClassesAndObjects a chapter of the notes |= translation of the main + personal heart ...
