Polymorphism php

<?php

	// class that extends abstract method must define all abstract declared methods

	/**
	 * Polymorphism describes a pattern in object oriented programming
	 * in which classes have different functionality while sharing a common interface.
	 * refer to http://net.tutsplus.com/tutorials/php/understanding-and-applying-polymorphism-in-php/
	 * http://www.easylearntutorial.com/2012/11/advanced-php-tutorial-what-is-polymorphism.html#.UeUwgkAyagZ
	 * 	 	OR
	 * page 44 of Object oriented Programming with php : PACKT
	 */


	abstract class Shape
	{
		private $_color = "black";
		private $_filled = false;

		public function getColor()
		{
			return $this->_color;
		}

		public function setColor( $color )
		{
			$this->_color = $color;
		}

		public function isFilled()
		{
			return $this->_filled;
		}

		public function fill()
		{
			$this->_filled = true;
		}

		public function makeHollow()
		{
			$this->_filled = false;
		}

		abstract public function getArea();  // define this method in any class that extends it

	}  // End of abstact class MyAbstract

	class Rectangle extends Shape
	{
		private $_width = 0;
		private $_height = 0;

		public function getWidth()
		{
			return $this->_width;
		}

		public function getHeight()
		{
			return $this->_height;
		}

		public function setWidth(  $width  )
		{
			$this->_width = $width;
		}

		public function setHeight( $height )
		{
			$this->_height = $height;
		}

		public function getArea()
		{
			return $this->_height * $this->_width;
		}

	}  // End of class Rectangle , extending Shape

	echo "<pre>";

	$r = new Rectangle();

	$r->setWidth(10);
	$r->setHeight(20);

	echo $r->getWidth() . "<br>" ;
	echo $r->getHeight() . "<br>" ;

	echo $r->getColor() . "<br>";
	$r->setColor("Green");
	echo $r->getColor()  . "<br>";

	var_dump( $r->isFilled() ) ;

	$r->fill();

	var_dump( $r->isFilled() ) ;

	$r->makeHollow();

	var_dump( $r->isFilled() ) ;

	echo"</pre>";
?>