The difference between public, private and protected in PHP

public, private and protected are called access modifiers. Just like C, PHP also has three access modifiers such as public, private and protected. The visibility of a property, method or constant can be defined by preceding the declaration with these keywords.

#1. If a class member is declared public, then it can be accessed from anywhere.

2. If a class member is declared protected, it can only be accessed within the class itself and in inheritance and parent classes.

3. If a class member is declared private, it can only be accessed by the class that defines the member.

public: This modifier can be used both internally and externally.

Example:

<?php

class pub {
    public $tag_line = "PHP中文网！";
    function display() {
        echo $this->tag_line."<br/>";
    }
}

class child extends pub {
    function show(){
        echo $this->tag_line;
    }
}

$obj= new child;

echo $obj->tag_line."<br/>";

$obj->display();

$obj->show();

Output:

PHP中文网！
PHP中文网！
PHP中文网！

protected: This modifier can be used in the class in which it is defined and its parent or inherited class .

Example:

<?php 
  
class pro { 
    protected $x = 500; 
    protected $y = 500; 
              
    function sub()  
    { 
        echo $sum=$this->x-$this->y . "<br/>"; 
    }      
}  
  
class child extends pro { 
    function mul() 
    { 
        echo $sub=$this->x*$this->y; 
    } 
}  
  
$obj= new child; 
$obj->sub(); 
$obj->mul(); 
?>

Output:

0 
250000

private: This modifier can be used in the class in which it is defined. (It cannot be accessed outside the class means inherited class).

Example:

<?php

class demo {
    private $name="PHP中文网";

    private function show()
    {
        echo "这是基(父)类的私有方法";
    }
}

class child extends demo {
    function display()
    {
        echo $this->name;
    }
}

$obj= new child;
$obj->show();
$obj->display();

Output: The error shown in the figure is because private class data cannot be accessed outside the class.

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