Section 7 - Static members of classes - Classes and Objects in PHP5 [7]_PHP Tutorial

Section 7 - Static members of a class
Static members of a class are different from ordinary 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 that the class wants to encapsulate, but Excludes the functionality and data of a specific object. 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 In addition to restricting access, the static properties of a class are very similar to the global variables of a function
We use a static property Counter::$count in the following example. It belongs to the Counter class and does not belong to any Counter instance. You cannot use this to refer to it, but you can use self or other valid naming expressions. In the example, the getCount method returns self::$count, not Counter::$count.
The static method implements the functions that the class needs to encapsulate, It has nothing to do with a specific object. Static methods are very similar to global functions. Static methods can fully access the properties of the class, or they can be accessed by instances of the object, regardless of the access qualifier.
In example 6.3, 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 create this variable inside static methods, even if you call them from an object.
Example 6.7 is derived from 6.3 changing getCount to a static method. The Static keyword cannot prevent an instance from using -> 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 - Constructor and Analysis The example in the constructor (see the previous article), by comparing the two examples, you can easily grasp the difference between
//static method and ordinary method.
You can write a method to determine whether this is established to show 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 attributes, 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
class Counter
{
private static $count = 0;
const VERSION = 2.0;
function __construct()
{
self: :$count++;

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