PHP inheritance

<?php

class Base
{
    public function testBase()
    {
        //var_dump(__METHOD__ . ' is ran from: ' . get_class($this));
        return $this->x;
    }
}

class Aclass extends Base
{
    private $x = __CLASS__;
    protected $y = __CLASS__;

    public function test()
    {
        echo "\tget_class(\$this): "  . get_class($this) . PHP_EOL;
        echo "\tget_class():" . get_class() . PHP_EOL;
        echo "\tmethod: " . __METHOD__ . PHP_EOL;
        echo "\t\$this->x: " . $this->x . PHP_EOL;
        echo "\t\$this->y: " . $this->y . PHP_EOL;

        // return static::$x; // Fatal error: Cannot access private property Bclass::$x
        return $this->x;
    }
}

class Bclass extends Aclass
{
    private $x = __CLASS__;
    protected $y = __CLASS__;
}


$bObj = new Bclass();
echo '$bObj = new Bclass();' . PHP_EOL;
echo 'get_class($bObj) => ' . get_class($bObj) . PHP_EOL;
echo '$bObj->test()' . PHP_EOL;
$bObj->test();

echo PHP_EOL;
echo '\\Closure::bind(function() { return $this->test(); }, new Aclass(), $bObj)->__invoke()' . PHP_EOL;
\Closure::bind(function() { return $this->test(); }, new Aclass(), $bObj)->__invoke();

echo PHP_EOL;

echo '\Closure::bind(function() { return $this->test(); }, $bObj, $bObj)->__invoke()' . PHP_EOL;
\Closure::bind(function() { return $this->test(); }, $bObj, $bObj)->__invoke();

echo PHP_EOL;

// PHP Fatal error:  Uncaught Error: Cannot access private property Aclass::$x
// $aObj = new Aclass();
// $aObj->testBase();

/**
OUTPUT:

$bObj = new Bclass();
get_class($bObj) => Bclass
$bObj->test()
    get_class($this): Bclass
    get_class():Aclass
    method: Aclass::test
    $this->x: Aclass
    $this->y: Bclass

\Closure::bind(function() { return $this->test(); }, new Aclass(), $bObj)->__invoke()
    get_class($this): Aclass
    get_class():Aclass
    method: Aclass::test
    $this->x: Aclass
    $this->y: Aclass

\Closure::bind(function() { return $this->test(); }, $bObj, $bObj)->__invoke()
    get_class($this): Bclass
    get_class():Aclass
    method: Aclass::test
    $this->x: Aclass
    $this->y: Bclass