PHP类定义方法

Question

Why in the method greet() must I not add a parameter $firstname in the declaration of the function?

Wrong:

    public function greet($firstname){
      echo "Bonjour, mon nom est ". $this->firstname . "Ravi de vous rencontrer ! :-)";
    }

Correct:

    class Person {
    public $isAlive = true;
    public $firstname;

    public function __construct($firstname,$lastname,$age){
        $this->firstname = $firstname;           
    }

    public function greet(){
        echo "Bonjour, mon nom est ". $this->firstname . "Ravi de vous rencontrer ! :-)";   
    }                
    }

Answer 1

If you do not declare ,

public $firstname; 

in the class, then it becomes a local variable,which cannot be accessed same as a class variable.