Object Model PHP 50 Object Model Deep Exploration of Static Members Like

　Static properties contain data to be encapsulated in a class and can be shared by all instances of the class. In fact, in addition to belonging to a fixed class and restricting access methods, the static properties of a class are very similar to the global variables of a function.
　We use a static property Counter::$count in the following example. It belongs to the Counter class and not to any instance of Counter. You cannot use this to refer to it, but you can use self or other valid naming expressions. In the example, the getCount method returns self::$count, not Counter::$count.
　 Static methods implement functions that need to be encapsulated by the class and have nothing to do with specific objects. Static methods are very similar to global functions. Static methods can fully access the attributes of the class or be accessed by instances of the object, regardless of whether the access qualifier is What.
In the previous example, getCount is an ordinary method, called with ->. PHP creates a this variable, although the method is not used. However, getCount does not belong to any object. In some cases, we even If you want to call it when there is no valid object, then you should use static methods. PHP will not create this variable inside static methods, even if you call them from an object.
　 Example 6.7 comes from 6.3 changing getCount to a static method. The Static keyword cannot prevent an instance from using the -> operator to call getCount, but PHP will not create this variable inside the method. If you use this-> to call, an error will occur.
//Example 6.3 refers to Section 4 --Examples in constructors and destructors (see the previous article). By comparing the two examples, you can have a good grasp of the difference between
//static methods and ordinary methods.
　You can write a method by judging this Whether established shows whether it is called statically or non-statically. Of course, if you use the static keyword, this method will always be static no matter how it is called.
Your class can also define constant properties, no need To use public static, just use the const keyword. Constant properties are always static. They are properties of the class, not the properties of the object that instantiates the class.
Listing 6.7 Static members

Copy code The code is as follows:

class Counter
{
private static $count = 0;
const VERSION = 2.0;
function __construct()
{
self::$count++;
}
function__destruct()
　{
　self: :$count--;
　}
static function getCount()
{
　return self::$count;
　}
};
//Create an instance, then __construct() will execute
$c = new Counter( );
//Output 1
print(Counter::getCount() . "n");
//Output the version attribute of the class
print("Version used: " . Counter::VERSION . "n");
?>

The above introduces the static members of the object model, PHP 50 object model in-depth exploration, including the content of the object model. I hope it will be helpful to friends who are interested in PHP tutorials.