《PHP对象、模式与实践》之高级特性

高级特性
包括：
1.静态方法和属性（通过类而不是对象来访问数据和功能）
2.抽象类和接口（设计，实现分离）
3.错误处理（异常）
4.Final类和方法（限制继承）
5.拦截器（自动委托）
6.析构方法（对象销毁前的清理工作）
7.克隆对象（创建对象的副本）
8.把对象解析成字符串

PS，学会从内存的角度看代码。想象计算机的微观世界。

静态方法的小例子

<?php
class StaticExample{
    static public $aNum = 10;
    static public function sayHello(){
        print "hello";
    }
}
print StaticExample::$aNum."<br/>";
StaticExample::sayHello();

tips:
1.静态方法不能访问类中的普通属性，因为那些属性属于一个对象，但可以访问静态属性。
2.我们不能再对象中调用静态方法，因此不能再静态方法中使用伪变量$this。

静态方法的大例子

<?php
class ShopProduct{
    private $title;
    private $producerMainName;
    private $producerFirstName;
    protected $price;
    private $discount = 0;
    private $id = 0;
    function __construct($title,$firstName,$mainName,$price){
        $this->title = $title;
        $this->producerFirstName = $firstName;
        $this->producerMainName = $mainName;
        $this->price = $price;
    }

    public function setID($id){
        $this->id = $id;
    }
    public static function getInstance($id,PDO $pdo){
        $query = "select * from products where id= '$id'";
        $stmt = $pdo->query($query);
        $row = $stmt->fetch();
        if(empty($row)){
            return null;
        }
        if($row['type'] == "book"){
            $product = new BookProduct($row['title'],
                $row['firstname'],
                $row['mainname'],
                $row['price'],
                $row['numpages']
                );
        }else if($row['type'] == "cd"){
            $product = new CdProduct($row['title'],
                $row['firstname'],
                $row['mainname'],
                $row['price'],
                $row['playLength']
                );
        }else{
            $product = new ShopProduct($row['title'],
                $row['firstname'],
                $row['mainname'],
                $row['price']
                );
        }
        $product->setId($row['id']);
        $product->setDiscount($row['discount']);
        return $product;
    }

    public function getProducerFirstName(){
        return $this->producerFirstName;
    }

    public function getProducerMainName(){
        return $this->producerMainName;
    }

    public function setDiscount($num){
        $this->discount = $num;
    }

    public function getDiscount(){
        return $this->discount;
    }

    public function getTitle(){
        return $this->title;
    }

    public function getPrice(){
        return ($this->price - $this->discount);
    }

    function getProducer(){
        return $this->producerFirstName." ".$this->producerMainName;
    }

    function getSummaryLine(){
        $base = "$this->title({$this->producerMainName},";
        $base .= "{$this->producerFirstName})";
        return $base;
    }
}

class CdProduct extends ShopProduct{
    private $playLength;
    function __construct($title,$firstName,$mainName,$price,$playLength){
        parent::__construct($title,$firstName,$mainName,$price);//继承父类的构造函数
        $this->playLength = $playLength;
    }

    function getPlayLength(){
        return $this->playLength;
    }

    function getSummaryLine(){
        $base = parent::getSummaryLine();
        $base .= ":playing time {$this->playLength}";
        return $base;
    }
}

class BookProduct extends ShopProduct{
    private $numPages = 0;
    function __construct($title,$firstName,$mainName,$price,$numPages){
        parent::__construct($title,$firstName,$mainName,$price);
        $this->numPages = $numPages;
    }
    function getnumPages(){
        return $this->numPages;
    }

    function getSummaryLine(){
        $base = parent::getSummaryLine();
        $base .= ":page count {$this->numPages}";
        return $base;
    }
}

$dsn = "sqlite:C:/Users/Administrator/Desktop/shop.db";
$pdo = new PDO($dsn,null,null);
$pdo->setAttribute(PDO::ATTR_ERRMODE,PDO::ERRMODE_EXCEPTION);
$obj = ShopProduct::getInstance(1,$pdo);
echo $obj->getSummaryLine();