Section 7 - Static members of classes_PHP tutorial

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Section 7 - Static members of class

class Static members are different from general class members: static members have nothing to do with the instance of the object, only the class itself. They are used to implement the functions and data to be encapsulated by the class, but do not include the functions and data of specific objects. Static members include static Methods and static properties.

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 Global variables similar to functions

We use a static property Counter::$count in the following example. It belongs to the Counter class and does not belong to any Counter instance. You cannot use this to refer to it, but you can Use self or other valid naming expressions. In the example, the getCount method returns self::$count, not Counter::$count.

Static methods implement the functions that the class needs to encapsulate, and specific objects Regardless. Static methods are very similar to global functions. Static methods can fully access the properties of the class, and can also be accessed by instances of the object, regardless of the access qualifier.

In the 6.3 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 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 a The example uses 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.

//6.3 Example 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 to show whether it is called statically or non-statically by determining whether this is created. 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. You don't 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++;                                                   

static function getCount( )
{ Counter();

//Output 1
print(Counter::getCount() . "
n");

//Output the version attribute of the class
print("Version used: " . Counter::VERSION . "
n");
?>




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/* +--------------------- -------------------------------------------------- --------+ |=This article is Haohappy's notes from the chapter ClassesandObjects when reading CorePHP Programming |=Translation is mainly + personal...