When to use $this->property instead of $property in PHP

Question

Super easy question. Look at the 2 sample class methods.

In the first One I pass in a variable/property call $params I then do $this->params

Answer 1

I hope this will help clear things up:

class Person {

   private $name;
   private $age;

   public function __construct($name, $age){
     // save func params to instance vars
     $this->name = $name;
     $this->age = $age;
   }

   public function say_hello(){ // look, no func params!
     echo "My name is {$this->name} and I am {$this->age} years old!";
   }

   public function celebrate_birthday(){ // no params again
     echo "Party time!";
     $this->age += 1; // update instance var
     $this->drink_beer();  // call instance method
   }

   public function drink_beer(){
     echo "Beer is good!";
   }
}

$p = new Person("Sample", "20");
$p->say_hello();          // My name is Sample and I am 20 years old!
$p->celebrate_birthday(); // Party time! Beer is good!
$p->say_hello();          // My name is Sample and I am 21 years old!