In PHP::, ->, self, $this operators

When accessing member variables or methods in a PHP class, if the referenced variable or method is declared as const (defining a constant) or static (declaring static), then you must use the operator::, otherwise if the referenced variable or method If the method is not declared const or static, the operator -> must be used.

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In addition, if you access a const or static variable or method from inside the class, you must use the self-referential self. On the contrary, if you access a non-const or static variable or method from the inside of the class, you must use the self-referenced $this.

$this instance

The code is as follows
<?php

// this is a pointer to the current object

class test_this{
private $content; //Define variables
​
Function __construct($content){ //Define constructor
            $this->cOntent= $content;
}
Function __destruct(){}//Define destructor
​
Function printContent(){//Define printing function
echo $this->content.’
‘;
}
}

$test=new test_this(‘Welcome to Beijing!’); //Instantiated object
$test->printContent();//Welcome to Beijing!
​

::Instructions

The code is as follows
//parent is a pointer to the parent class

class test_parent{ //base class
Public $name; //Define name Parent class members need to be defined as public before they can be called directly using this in the inherited class.
Function __construct($name){
           $this->name=$name;
}
}
class test_son extends test_parent{ // Derived class inherits test_parent
Public $gender;//Define gender
Public $age; //Define age
Function __construct($gender,$age){ //Inherit the constructor of the class
parent::__construct(‘nostop’);//Use parent to call the constructor of the parent class to instantiate the parent class
           $this->gender=$gender;
          $this->age=$age;
}
Function __destruct(){}
Function print_info(){
echo $this->name.’ is a ‘.$this->gender.’, this year is ‘.$this->age.’.’
‘;
}
}

$nostop=new test_son(‘female’,’22’);//Instantiate the test_son object
$nostop->print_info();//Execute the output function nostop is a female, 23 years old this year
​

Use the form self::$name. Note that the declaration format of the const attribute is const PI=3.14, not const $PI=3.14

The code is as follows
class clss_a {
         
Private static $name=”static class_a”;
         
Const PI=3.14;
Public $value;
                                                                 
Public static function getName()
{
           return self::$name;                                    
}
//This way of writing is wrong, static methods cannot access non-static properties
Public static function getName2()
{
           return self::$value;
}
Public function getPI()
{
         return self::PI;                               
}
         
         
}
​

Another thing to note is that if a class method is static, the properties it accesses must also be static.
The internal method access of the class is not declared as const and static