A detailed explanation of the differences between this, self, and parent in PHP_PHP Tutorial

classcounter //Define a counter class
{
//Define attributes, including a static variable $firstCount, and assign an initial value of 0 Statement ①
private static $firstCount = 0;
private $lastCount;
//Constructor function
function __construct()
{
lastCount =++self::$firstCount; //Use self to call the static variable statement ②
}
}
}
//Instantiate the object
$obj = new Counter();
$obj->printLastCount(); >


There are two places to pay attention to here, sentence ① and sentence ②. We defined a static variable $firstCount in statement ①, and then used self to call this value in statement ②. Then what we call at this time is the static variable $frestCount defined by the class itself. Our static variable has nothing to do with the instance of the following object, it is only related to the class. Then if I call the class itself, then we cannot use this to refer to it, because self points to the class itself and has nothing to do with any object instance. Then the this used earlier calls the instantiated object $obj, so don’t get confused.
That’s it for self. It’s easier to understand with examples. The end of the second chapter.

public $name; //Attributes of the base class, name $name
//Constructor of the base class, initialization assignment
public function __construct( $name )
{
                                                                                          using using using  -                                                                                                       ’ ’ s ’ s ’ s ’ ’ s use to ward through so so so so so so so so so so so out out out out out out out out out out out out out out out out out of         and                  out. $personSex; //For derived classes, newly defined attributes $personSex gender, $personAge age
public $personAge;
//Constructor of derived classes
function __construct( $personSex, $personAge)
{
parent::__construct( "PBPHome"); // Use parent to call the constructor statement of the parent class ①
$this->personSex = $personSex;
$this-> personAge = $personAge;
}
//Member function of the derived class, used for printing, format: name is name, age is age
function printPerson()
{
print( $ this->name. " is ".$this->personSex. ",age is ".$this->personAge );
}
}
//Instantiate the Person object
$personObject = new Person( "male", "21");
//Perform printing
$personObject->printPerson();//Output result: PBPHome is male,age is 21
?>


It also contains the usage of this, please analyze it yourself. We pay attention to this detail: the member attributes are all public (public attributes and methods, accessible to code inside and outside the class), especially those of the parent class. This is for inherited classes to access through this. The key point is statement ①: parent::__construct("heiyeluren"). At this time, we use parent to call the constructor of the parent class to initialize the parent class. In this way, the objects of the inherited class are assigned the name PBPHome. . We can test it by instantiating another object $personObject1. After printing, the name is still PBPHome.
Summary: this is a pointer to an object instance, which is determined when instantiating; self is a reference to the class itself, generally used to point to static variables in the class; parent is a reference to the parent class, Generally, parent is used to call the constructor of the parent class.