OOP Basics

/**
 * Instances CANNOT use private and protected members
 * Children CAN inherit only public and protected members
 */
class MyClass
{
    public $name = 'John';
    protected $username = 'JohnT23';
    private $password = 'secret';

    function printAll()
    {
        echo "From class MyClass:";
        echo $this->name." ";
        echo $this->username." ";
        echo $this->password." ";
    }
}

$obj = new MyClass();
echo "From Instance \$obj:".$obj->name."\n"; //Works
//echo $obj->username; // Fatal Error
//echo $obj->password; // Fatal Error
$obj->printAll();

echo"\n<br>";

class MyClass2 extends MyClass
{
    // We can re-declare/access the public and protected method
    // but not private ones
    function printAll()
    {
        echo "From class MyClass2:";
        echo $this->name." ";
        echo $this->username." ";
        // Children cannot access private member of parent
        // echo $this->password; // Error
    }
}

$obj2 = new MyClass2();
echo "<br>
 From Instance \$obj2:".$obj2->name; // Works
//echo $obj->username; // Fatal Error
//echo $obj->password; // Fatal Error
$obj2->printAll();