PHP继承 - 具有子属性的父函数

Question

Using PHP 5.4 - Company won't upgrade because it would break existing code. Sorry about that.

Say I have a class Resource:

class Resource {
  private $resourceIdentifier;

  public function __construct() {
    $this->resourceIdentifier = "ResourceId";
  }

  public function getIdentifier() {
    return $this->resourceIdentifier;
  }
}

Then, that class has a child:

class Employee extends Resource {
  public function __construct() {
    $this->resourceIdentifier = "EmployeeId";
  }
}

Then I create an instance of employee and call getIdentifier()

$emp = new Employee();
echo $emp->getIdentifier();

Will the function return $resourceIdentifier from the parent or the child?

On top of that, what will happen if I don't define $resourceIdentifier in the parent but I do in the child?

class Resource {
  public function getIdentifier() {
    return $this->resourceIdentifier;
  }
}

class Employee extends Resource {
  private $resourceIdentifier;

  public function __construct() {
    $this->resourceIdentifier = "EmployeeId";
  }
}

Answer 1

If the $resourceIdentifier attribute is private, then the parent class cannot access it. You need to make it protected instead:

class Employee extends Resource {
  protected $resourceIdentifier;

  public function __construct() {
    $this->resourceIdentifier = "EmployeeId";
  }
}