A simple comparison of public, private and protected in PHP

There are three access modifiers in PHP: public, private and protected. You can define the visibility of properties, methods or constants by adding these keywords before the declaration. So what's the difference between them? Here is a brief introduction in this article, I hope it will be helpful to everyone.

PHP public access modifier

The public modifier can be used both internally and externally. If a class member is declared public, it can be accessed from anywhere. [Video tutorial recommendation: PHP tutorial]

Example:

<?php 
header("content-type:text/html;charset=utf-8");  
// BaseClass 
class pub { 
    public $tag_line = "php中文网！"; 
    function display() { 
        echo $this->tag_line."<br/>"; 
    } 
} 
  
// 子类
class child extends pub { 
    function show(){ 
        echo $this->tag_line; 
    } 
}  
  
// 对象声明
$obj= new child; 
  
// 输出
echo $obj->tag_line."<br/>";  
  
$obj->display();  
  
$obj->show();  
?>

Output:

private access modifier

The private modifier can be used in the class in which it is defined and its parent or inherited classes. If a class member is declared protected, it can only be accessed within the class itself and from inheritance and parent classes.

Example:

<?php 
header("content-type:text/html;charset=utf-8");  
// 基类
class pro { 
    protected $x = 500; 
    protected $y = 500; 
              
    // 实现减法 
    function sub()  
    { 
        echo $sum=$this->x-$this->y . "<br/>"; 
    }      
}  
  
// 子类-继承类
class child extends pro { 
    function mul() //实现乘法
    { 
        echo $sub=$this->x*$this->y; 
    } 
}  
  
$obj= new child; 
$obj->sub(); 
$obj->mul(); 
?>

Output:

protected access modification The

#protected modifier can be used in the class in which it is defined. Note: It cannot be accessed outside the class means inherited classes.

If a class member is declared private, it can only be accessed by the class in which the member is defined.

Example:

<?php 
header("content-type:text/html;charset=utf-8");  
// 基类
class demo { 
    private $name="PHP中文网！"; 
      
    private function show() 
    { 
        echo "这是基类的私有方法"; 
    } 
}  
  
// 子类
class child extends demo { 
    function display() 
    { 
        echo $this->name; 
    } 
}  
  
// 对象声明
$obj= new child; 
  
// 出现异常---未捕获错误：调用私有方法demo：：show()
//$obj->show();  
  
//出现异常--未定义的属性：子级：：$name
$obj->display(); 
?>

Output

:

Explanation:

As you can see from the above example, it will show an error because private class data cannot be accessed outside the class.

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