Detailed explanation of the differences and usage of this, self, and parent keywords in php

{一}One of the differences between this, self, parent in PHP this article

Object-oriented programming (OOP, Object Oriented Programming) has now become a basic skill for programmers . Using OOP ideas for advanced programming of PHP is very meaningful for improving PHP programming capabilities and planning web development architecture. After being rewritten, PHP5 has made a big leap in its support for OOP and has become a language with most of the features of an object-oriented language. It has many more object-oriented features than PHP4. What I am mainly talking about here is the difference between the three keywords this, self, and parent. Literally understood, they refer to this, myself, and father respectively. Let me give a preliminary explanation first. This is a pointer to the current object (can be regarded as a pointer in C), self is a pointer to the current class, and parent is a pointer to the parent class. We frequently use pointers to describe here because there is no better language to express it. Regarding the concept of pointers, you can refer to the encyclopedia.
Let’s talk about it based on actual examples.

The code is as follows:

<?php
  classname          //建立了一个名为name的类
 {
    private$name;         //定义属性，私有
    //定义
构造函数
，用于初始化赋值
    function construct( $name )
    {
         $this->name =$name;         //这里已经使用了this指针语句①
    }
    //
析构函数
    function destruct(){}
    //打印用户名成员函数
    function printname()
    {
         print( $this->name);             //再次使用了this指针语句②，也可以使用echo输出
    }
 }
 $obj1 = new name("PBPHome");   //实例化对象 语句③
 //执行打印
 $obj1->printname(); //输出:PBPHome
 echo"<br>";                                    //输出：回车
 //第二次实例化对象
 $obj2 = new name( "PHP" );
 //执行打印
 $obj2->printname();                         //输出：PHP
 ?>

Explanation: The above class uses this pointer in statement ① and statement ② respectively, then at that time Who does this point to? In fact, this determines who it points to when instantiating it. For example, when the object is instantiated for the first time (statement ③), then this points to the $obj1 object at that time. Then when executing the print of statement ②, print( $this- >name ), then of course "PBPHome" is output. In the second instance, print($this->name) becomes print($obj2->name), so "PHP" is output. Therefore, this is a pointer to the current object instance and does not point to any other object or class.
{二}The difference between this, self and parent in PHP Part 2 self

In this article we will explain the usage of self

First of all we have to make it clear that self refers to the class Itself, that is, self does not point to any instantiated object. Generally, self is used to point to static variables in the class. If we use static members in the class (usually using the keyword static), we must also use self to call. Also note that using self to call static variables must use:: (field
operator ), see example.

The code is as follows:

<?php
    classcounter     //定义一个counter的类
    {
        //定义属性，包括一个静态变量$firstCount，并赋初值0 语句①  
        private static $firstCount = 0;
        private $lastCount;
        //构造函数
        function construct()
        {
             $this->lastCount =++self::$firstCount;      //使用self来调用静态变量 语句②
        }
        //打印lastCount数值
        function printLastCount()
        {
             print( $this->lastCount );
        }
    }
  //实例化对象
  $obj = new Counter();
 $obj->printLastCount();                             //执行到这里的时候，程序输出1
 ?>

There are two places to pay attention to here: statement ① and statement 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.

{三}The difference between this, self and parent in PHP Part 3 parent

In this article we will explain the usage of parent.

First of all, we make it clear that parent is a pointer to the parent class. Generally, we use parent to call the constructor of the parent class. The example is as follows:

The code is as follows:

<?php
 //建立基类Animal
 class Animal
 {
    public $name; //基类的属性，名字$name
    //基类的构造函数，初始化赋值
    public function construct( $name )
    {
         $this->name = $name;
    }
 }
 //定义派生类Person 继承自Animal类
 class Person extends Animal
 {
    public$personSex;       //对于派生类，新定义了属性$personSex性别、$personAge年龄
    public $personAge;
    //派生类的构造函数
    function construct( $personSex, $personAge )
    {
         parent::construct( "PBPHome");    //使用parent调用了父类的构造函数 语句①
         $this->personSex = $personSex;
         $this->personAge = $personAge;
    }
    //派生类的成员函数，用于打印，格式：名字 is name,age is 年龄
    function printPerson()
    {
         print( $this->name. " is ".$this->personSex. ",age is ".$this->personAge );
     }
 }
 //实例化Person对象
 $personObject = new Person( "male", "21");
 //执行打印
 $personObject->printPerson();//输出结果：PBPHome is male,age is 21
 ?>

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. access. 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.

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