PHP5.0对象模型探索之抽象方法和抽象类

/*注:
两种方法即指:
1. abstract class aaa{} (注意aaa中只有抽象方法，没有一般方法)
class bbb extends aaa{} (在bbb中覆写aaa中的抽象方法)
2. interface aaa{}
class bbb implements aaa{} (在bbb中覆写aaa中的抽象方法)
*/

listing 6.13 abstract classes

//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");
}

?＞