php public private protected

public Global representation , Class internal and external subclasses can access ;
private For private , Only this class can be used internally ;
protected Indicates protected , Only this class or subclass or parent class can access ;

   <?
    // Parent class 
    class father{
    
     public function a(){
    
      echo "function a";
     }
     private function b(){
    
      echo "function b";
     }
     protected function c(){
    
      echo "function c";
     }
    }
    // Subclass 
    class child extends father{
    
      function d(){
    
        parent::a();// Calling the a Method 
      }
      function e(){
    
       parent::c(); // Calling the c Method 
      }
     function f(){
    
        parent::b(); // Calling the b Method 
      }
    }
    $father=new father();
    $father->a();
    $father->b(); // Display error   External cannot call private method  Call to protected method father::b()
    $father->c(); // Display error   Protected methods cannot be called externally Call to private method father::c()
    $chlid=new child();
    $chlid->d();
    $chlid->e();
    $chlid->f();// Display error   Cannot call parent class private Methods  Call to private method father::b()
    ?>