php 类中多态的应用
php教程 类中多态的应用
Instanceof:用来测定一个给定的对象是否来自指定的对象类
class A{}
class B{}
$thing=new A();
//return true
if ($thing instanceof A) {
echo 'A';
}
//return false
if ($thing instanceof B) {
echo 'B';
}
?>
运行结果:
A
header("Content-Type:text/html;charset=UTF-8");
interface MyUsb{
function type();
function alert();
}
class Zip implements MyUsb{
function type(){
echo "2.0";
}
function alert(){
echo "正在检查U盘驱动";
}
}
class Mp3 implements MyUsb{
function type(){
echo "1.0";
}
function alert(){
echo "正在检查Mp3驱动";
}
}
class Mypc{
function PcUsb($what)
{
$what->type();
$what->alert();
}
}
$pc=new Mypc();
$zip=new Zip();
$mp3=new Mp3();
$pc->PcUsb($zip);//当插上的是U盘的时候
echo "
";
$pc->PcUsb($mp3);//当插上的是MP3的时候
?>
运行结果:
2.0正在检查U盘驱动
1.0正在检查Mp3驱动
对象引用都是一样的不分父类引用,还是子类引用。 我们现在来看一个例子,首先还是要使用多态就要有父类对象和子类对象的关系。做一 个形状的接口或是抽象类做为父类,里面有两个抽象方法,一个求周长的方法,另一个是求 面积的方法;这接口的子类是多种不同的形状,每个形状又都有周长和面积,又因为父类是 一个接口,所以子类里面就必须要实现父类的这两个周长和面积的抽象方法,这样做的目的 是每种不同形状的子类都遵守父类接口的规范,都要有求周长和求面积的方法。
代码如下:
//定义了一个形状的接口,里面有两个抽象方法让子类去实现
interface Shape{
function area();
function perimeter();
}
//定义了一个矩形子类实现了形状接口中的周长和面积
class Rect implements Shape{
private $width;
private $height;
function __construct($width, $height){
$this->width=$width;
$this->height=$height;
}
function area(){
return "矩形的面积是:".($this->width*$this->height);
}
function perimeter(){
return "矩形的周长是:".(2*($this->width+$this->height));
}
}
//定义了一个圆形子类实现了形状接口中的周长和面积
class Circular implements Shape{
private $radius;
function __construct($radius){
$this->radius=$radius;
}
function area(){
return "圆形的面积是:".(3.14*$this->radius*$this->radius);
}
function perimeter(){
return "圆形的周长是:".(2*3.14*$this->radius);
}
}
//把子类矩形对象赋给形状的一个引用
$shape=new Rect(5, 10);
echo $shape->area()."
";
echo $shape->perimeter()."
";
//把子类圆形对象赋给形状的一个引用
$shape=new Circular(10);
echo $shape->area()."
";
echo $shape->perimeter()."
";
?>
上例执行结果:
执行结果
矩形的面积是:50
矩形的周长是:30
圆形的面积是:314
圆形的周长是:62.8
通过上例我们看到,把矩形对象和圆形对象分别赋给了变量$shape,调用$shape 引用中
的面积和周长的方法,出现了不同的结果,这就是一种多态的应用,其实在我们PHP 这种弱
类形的面向对象的语言里面,多态的特性并不是特别的明显,其实就是对象类型变量的变项
应用。

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