Ring queue PHP

<?php

#  The circular queue php
class queue
{
    
    public $queue = [];
    public $size;
    public $front = 0; #  Pointer to the first team 
    public $rear = 0; #  Pointer to a party 

    public function __construct($size = 10)
    {
    
        $this->size = $size;
        for ($i = 0; $i < $this->size; $i++) {
    
            $this->queue[] = '';
        }
    }

    #  List 
    public function push($element)
    {
    
        if (!$this->is_filled()) {
    
            $this->rear = ($this->rear + 1) % $this->size;
            $this->queue[$this->rear] = $element;
        } else {
    
            throw new Exception(" The queue is full ");
        }
    }

    #  List out 
    public function pop()
    {
    
        if (!$this->is_empty()) {
    
            $this->front = ($this->front + 1) % $this->size;
            $element = $this->queue[$this->front];
            $this->queue[$this->front] = '';
            return $element;
        } else {
    
            throw new Exception(" The queue is empty ");
        }
    }

    #  Determines if the queue is empty 
    public function is_empty()
    {
    
        return $this->rear == $this->front;
    }

    #  Determine whether the queue is full 
    public function is_filled()
    {
    
        return ($this->rear + 1) % $this->size == $this->front;
    }

    public function get_queue()
    {
    
        return $this->queue;
    }
}

// Declaration stack 
$queue = new queue(6);
$queue->push(5);
$queue->push(6);
$queue->push(7);
$queue->push(8);
$queue->push(9);

$queue->pop();
$queue->pop();
$queue->pop();

$queue->push(10);
$queue->push(11);
$queue->push(12);


print_r($queue->get_queue());