抽象方法和抽象类_PHP教程

＜?php    //abstract root class 抽象根类    abstract class Shape    {        abstract function getArea(); //定义一个抽象方法    }    //abstract child class 抽象子类    abstract class Polygon extends Shape //多边形    {        abstract function getNumberOfSides();    }    //concrete class 实体类 三角形类    class Triangle extends Polygon    {        public $base;        public $height;        public function getArea() //覆写计算面积方法        {            return(($this->base * $this->height)/2);        }        public function getNumberOfSides() //覆写边数统计方法        {            return(3);        }    }    //concrete class 实体类四边形    class Rectangle extends Polygon    {        public $width;        public $height;        public function getArea()        {            return($this->width * $this->height);        }        public function getNumberOfSides()        {            return(4);        }    }    //concrete class 实体类 圆形    class Circle extends Shape    {        public $radius;        public function getArea()        {            return(pi() * $this->radius * $this->radius);        }    }    //concrete root class 定义一个颜色类    class Color    {        public $name;    }    $myCollection = array(); //建立形状的集合,放入数组    //make a rectangle    $r = new Rectangle;    $r->width = 5;    $r->height = 7;    $myCollection[] = $r;    unset($r);    //make a triangle    $t = new Triangle;    $t->base = 4;    $t->height = 5;    $myCollection[] = $t;    unset($t);    //make a circle    $c = new Circle;    $c->radius = 3;    $myCollection[] = $c;    unset($c);    //make a color    $c = new Color;    $c->name = "blue";    $myCollection[] = $c;    unset($c);    foreach($myCollection as $s)    {        if($s instanceof Shape) //如果$s是Shape类的实例        {            print("Area: " . $s->getArea() .                "
n");        }        if($s instanceof Polygon)        {            print("Sides: " .                $s->getNumberOfSides() .                "
n");        }        if($s instanceof Color)        {            print("Color: $s->name
n");        }        print("
n");    } ?＞