Static members such as deep exploration of PHP 5.0 object model_PHP tutorial

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 access What is the qualifier?

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 want to call it when there is no valid object, then static methods should be used. PHP will not establish 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 Calling will cause an error.

//The 6.3 example refers to the example in Section 4 - Constructor and Destructor (see the previous article). By comparing the two examples, you can have a good grasp of it
//The difference between static methods and ordinary methods.

You can write a method to show whether it is called statically or non-statically by judging whether this is established. Of course, if you use the static key word, no matter how it is called, this method is always static.

Your class can also define constant properties. There is 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 Code As follows:

class Counter
{
private static $count = 0;
const VERSION = 2.0;

function __construct()
{
Self::$count++;
}

function __destruct()
{
self::$count--; ()
{
return self::$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");
?>

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www.bkjia.comtruehttp: //www.bkjia.com/PHPjc/318829.htmlTechArticleStatic 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...