php入门教程之面向对象-php教程

第一种情况：子类没有定义构造函数时，默认继承。

第二种情况：子类定义了构造函数，则不会被继承。

对于4.x,如果父类恰好定义了子类的同名函数，则会被当做子类的构造函数,实例代码如下:

class A
{
function A()
{
echo "I am the constructor of A. n";
}
function B()
{
echo "I am a regular function named B in class A. n";
echo "I am not a constructor in A. n";
}
}
class B extends A
{
function C()
{
echo "I am a regular function. n";
}
}
//php4 will call B()
$b = new B;

上面的代码在php5中则会调用A而不会调用B()

PHP面向对象:接口实例

我们设计一个在线销售系统，用户部分设计如下,将用户分为，NormalUser, VipUser, InnerUser三种,要求根据用户的不同折扣计算用户购买产品的价格,并要求为以后扩展和维护预留空间,用户部分先声明了一个接口User,用户都是User的实现。

user.php代码如下:

<?
/*
* 定义了 User接口.
* 和子类 NormalUser,VipUser,InnerUser
*/
//User接口,定义了三个抽象方法.
interface User{
public function getName();
public function setName($_name);
public function getDiscount();
}
abstract class AbstractUser implements User{
private $name = ""; //名字
protected $discount = 0; //折扣
protected $grade = ""; //级别
public function __construct($_name){
$this->setName($_name);
}
public function getName(){
return $this->name;
}
public function setName($_name){
$this->name = $_name;
}
public function getDiscount(){
return $this->discount;
}
public function getGrade(){
return $this->grade;
}
}
class NormalUser extends AbstractUser {
protected $discount = 1.0;
protected $grade = "NormalUser";
}
class VipUser extends AbstractUser {
protected $discount = 0.8;
protected $grade = "VipUser";
}
class InnerUser extends AbstractUser {
protected $discount = 0.7;
protected $grade = "InnerUser";
}
?>

关于产品,我们进行了如下设计,声明一个接口Product,然后从Product继承下Book接口,在线销售的图书最后是实现了Book接口的BookOnline类。

Product.php代码如下:

<?
/*与产品相关的类放.*/
Interface Product{ //定义产品接口
public function getProductName();
public function getProductPrice();
}
interface Book extends Product { // book是产品的一个分类
public function getAuthor();
}
class BookOnline implements Book{ // 定义book类.
private $productName; // 产品名
private $productPrice; // 产品价格
private $author; //作者
public function __construct($_bookName){
$this->productName = $_bookName;
//这里放置相关初始化的代码.
//与数据库关联的代码.
}
public function getProductName(){
return $this->productName;
}
public function getProductPrice(){
//这里从数据库读取价格.
//假设价格是 100元.
$this->productPrice = 100;
return $this->productPrice;
}
public function getAuthor(){
//从数据库里面取值.
return $this->author;
}
}
?>

关于结算,我们使用了独立的结算类,使用静态方法做计算,产品结算,注意参数类型,代码如下:

<?
include_once("User.php");
include_once("Product.php");
//买了产品到底多少钱呢?
class ProductSettle{
public static function finalPrice(User $_user,Product $_product,$number = 1){
$price = $_user->getDiscount() * $_product->getProductPrice() * $number;
return $price;
}
}
?>

下面的例子是实现,大家可以自己分析下,实例代码如下:

<?
include_once("./class/User.php");
include_once("./class/Product.php");
include_once("./class/ProductSettle.php");
$number = 10;
$book = new BookOnline("设计模式");
$user = new NormalUser("Tom");
$price = ProductSettle::finalPrice($user,$book,$number);
$str = "您好，尊敬的用户 " . $user->getName() . " ";
$str .= "您的级别是 ". $user->getGrade() .", ";
$str .= "您的折扣是 " . $user->getDiscount() . " ";
$str .= "购买 $number 本《 ". $book->getProductName() ;
$str .= "》的价格是 $price ";
echo $str;
$user = new vipUser("Tom");
$price = ProductSettle::finalPrice($user,$book,$number);
$str = "您好，尊敬的用户 " . $user->getName() . " ";
$str .= "您的级别是 ". $user->getGrade() .", ";
$str .= "您的折扣是 " . $user->getDiscount() . " ";
$str .= "购买 $number 本《 ". $book->getProductName() ;
$str .= "》的价格是 $price ";
echo $str;
$user = new InnerUser("Tom");
$price = ProductSettle::finalPrice($user,$book,$number);
$str = "您好，尊敬的用户 " . $user->getName() . " ";
$str .= "您的级别是 ". $user->getGrade() .", ";
$str .= "您的折扣是 " . $user->getDiscount() . " ";
$str .= "购买 $number 本《 ". $book->getProductName() ;
$str .= "》的价格是 $price ";
echo $str;
?>

php入门教程之面向对象

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