$animal = new Animal();

echo property_exists($animal, 'name'); // → 1
echo property_exists($animal, 'age');//  → 1
echo property_exists($animal, 'power');//  → 1
echo property_exists($animal, 'bark');//  → 空
echo property_exists($animal, 'dummy');// → 空

class Animal{
	public $name = 'Cat';
	protected $age = 99;
	private $power = 99;
	
	public function bark(){
		
	}
}
111