PHP two-way queue, double-ended queue code

/**
 * User: jifei
 * Date: 2013-07-30
 * Time: 23:12
*/
/**
 * PHP implements two-way queue, double-ended queue
 * A double-ended queue (deque, full name double-ended queue) is a data structure with queue and stack properties.
 * Elements in a double-ended queue can be popped from both ends, and insertion and deletion operations are limited to both sides of the queue.
*/
class Deque
{
    public $queue=array();
    /**
 * Constructor initializes the queue
*/
    public function __construct($queue=array())
    {
        if(is_array($queue))
        {
            $this->queue=$queue;
        }
    }
    /**
 * Get the first element
*/
    public function front()
    {
        return reset($this->queue);
    }
    /**
 * Get the last element
*/
    public function back()
    {
        return end($this->queue);
    }
    /**
 * Determine whether it is empty
*/
    public function is_empty()
    {
       return empty($this->queue);
    }
    /**
 * Queue size
*/
    public function size()
    {
       return count($this->queue);
    }
    /**
 * Insert to end
*/
    public function push_back($val)
    {
        array_push($this->queue,$val);
    }
    /**
 *Insert to the end
*/
    public function push_front($val)
    {
       array_unshift($this->queue,$val);
    }
    /**
 * Remove the last element
*/
    public function pop_back()
    {
       return array_pop($this->queue);
    }
    /**
 * Remove the first element
*/
    public function pop_front()
    {
        return array_shift($this->queue);
    }
    /**
 * Clear the queue
*/
    public function clear()
    {
        $this->queue=array();
    }
}
//初始化一个双向队列
$deque=new Deque(array(1,2,3,4,5));
echo $deque->size().PHP_EOL;
echo $deque->is_empty().PHP_EOL;
echo $deque->front().PHP_EOL;
echo $deque->back().PHP_EOL;
echo PHP_EOL;
//弹出元素测试
echo $deque->pop_back().PHP_EOL;
echo $deque->pop_front().PHP_EOL;
echo $deque->size().PHP_EOL;
echo PHP_EOL;
$deque->push_back('a').PHP_EOL;
$deque->push_front(0).PHP_EOL;
echo PHP_EOL;
//插入测试
echo $deque->front().PHP_EOL;
echo $deque->back().PHP_EOL;
echo $deque->size().PHP_EOL;
echo PHP_EOL;
//清空测试
$deque->clear();
echo $deque->is_empty();

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