《PHP对象、模式与实践》之对象

1.php与对象

知识点：

a.关于引用赋值

$other = &$my_obj;
//按照引用复制，指向相同对象。

例子：

<?php
$my_obj = 1;
echo $my_obj."<br/>";//１
$other = &$my_obj;
echo $other."<br/>";//
$my_obj = 2;
echo $other;//2
//按照引用复制，指向相同对象。

2.类与对象

知识点

a.类是对象的模板，对象是类实现的实例

变量函数对应类中的属性和方法。

和函数不同的是，方法必须在类体中声明。

$this是伪变量，可以将类指向一个对象实例。

b.一个类实例

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

    function getProducer(){
        return $this->producerFirstName." ".$this->producerMainName;
    }
}
$product1 = new ShopProduct("My pro","Willa","Tom",5.99);
print "author:{$product1->getProducer()}\n";

输出：

author:Willa Tom

一个更复杂的例子

<?php
class CdProduct{
    public $playLength;
    public $title;
    public $producerMainName;
    public $producerFirstName;
    public $price;
    function __construct($title,$firstName,$mainName,$price,$playLength){
        $this->title = $title;
        $this->producerFirstName = $firstName;
        $this->producerMainName = $mainName;
        $this->price = $price;
        $this->playLength = $playLength;
    }

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

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

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

class BookProduct{
    public $numPages;
    public $title;
    public $producerMainName;
    public $producerFirstName;
    public $price;
    function __construct($title,$firstName,$mainName,$price,$numPages){
        $this->title = $title;
        $this->producerFirstName = $firstName;
        $this->producerMainName = $mainName;
        $this->price = $price;
        $this->numPages = $numPages;
    }

    function getnumPages(){
        return $this->numPages;
    }

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

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

class ShopProduct{
    public $title;
    public $producerMainName;
    public $producerFirstName;
    public $price = 0;
    function __construct($title,$firstName,$mainName,$price){
        $this->title = $title;
        $this->producerFirstName = $firstName;
        $this->producerMainName = $mainName;
        $this->price = $price;
    }
　　
　　 function getSummaryLine(){ 
       $base = "{$this->title}({$this->producerMainName},";
       $base .= "{$this->producerFirstName})"; 
       return $base; 
    }
    function getProducer(){
        return $this->producerFirstName." ".$this->producerMainName;
    }
}
$product1 = new ShopProduct("My pro","Willa","Tom",5.99);
print "author:{$product1->getProducer()}<br/>";

$product2 = new CdProduct("My pro","Willa","Tom",5.99,1);
print "PlayLength:{$product2->getPlayLength()}<br/>";

$product3 = new BookProduct("My pro","Willa","Tom",5.99,10);
print "numPages:{$product3->getnumPages()}<br/>";

结果：

author:Willa Tom
PlayLength:1
numPages:10

点评：这三个类写在同一个文件下面，说明php支持一个文件包含多个类。只是这样有点不太好，最好单独一个文件，把他们引入进来，然后创建对象，使用。

这三个类还有一个缺点就是，代码重复了，每个类中都有getSummaryLine()方法，和getProducer()方法。这样就冗余了，这个时候怎么办呢？

如果类之间有一定的继承关系，可以用继承这种机制，当然也不要继承很多层次，那样太深了也不好。

适当的继承能够让类更简洁，更利索！

下面是继承的案例：

<?php
class ShopProduct{
    public $numPages;
    public $playLength;
    public $title;
    public $producerMainName;
    public $producerFirstName;
    public $price;
    function __construct($title,$firstName,$mainName,$price,$numPages=0,$playLength=0){
        $this->title = $title;
        $this->producerFirstName = $firstName;
        $this->producerMainName = $mainName;
        $this->price = $price;
        $this->numPages = $numPages;
        $this->playLength = $playLength;
    }

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

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

class CdProduct extends ShopProduct{
    function getPlayLength(){
        return $this->playLength;
    }

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

class BookProduct extends ShopProduct{
    function getnumPages(){
        return $this->numPages;
    }

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

$product1 = new ShopProduct("My pro","Willa","Tom",5.99);
print "SummaryLine:{$product1->getSummaryLine()}<br/>";

$product2 = new CdProduct("My pro","Willa","Tom",5.99,null,5);
print "SummaryLine:{$product2->getSummaryLine()}<br/>";

$product3 = new BookProduct("My pro","Willa","Tom",5.99,10,null);
print "SummaryLine:{$product3->getSummaryLine()}<br/>";

结果：

SummaryLine:My pro(Tom,Willa)
SummaryLine:My pro(Tom,Willa):playing time 5
SummaryLine:My pro(Tom,Willa):page count 10

点评：子类继承父类的属性和构造行数，以及一些基本的函数。

继承之后，可以覆盖父类的函数，也可以新建自己的函数。继承可以避免类内容的重复，代码的重复。

继续改造，子类中也有自己的构造方法。
在子类中定义构造方法时，需要传递参数给父类的构造方法，否则你得到的可能是一个构造不完整的对象。

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

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

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

class CdProduct extends ShopProduct{
    public $playLength;
    function __construct($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(){
        $base = "{$this->title}({$this->producerMainName},";
        $base .= "{$this->producerFirstName})";
        $base .= ":playing time {$this->playLength}";
        return $base;
    }
}

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

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

$product1 = new ShopProduct("My pro","Willa","Tom",5.99);
print "SummaryLine:{$product1->getSummaryLine()}<br/>";

$product2 = new CdProduct("My pro","Willa","Tom",5.99,5);
print "SummaryLine:{$product2->getSummaryLine()}<br/>";

$product3 = new BookProduct("My pro","Willa","Tom",5.99,10);
print "SummaryLine:{$product3->getSummaryLine()}<br/>";

结果同上一个效果一点，这里面每个子类都有自己的构造方法了，同时继承了父类中的构造方法。这样就保证了子类的灵活性。不完全受制于父类。

进一步添加访问权限设置，

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

    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;
    }
}

$product1 = new ShopProduct("My pro","Willa","Tom",5.99);
print "SummaryLine:{$product1->getSummaryLine()}<br/>";

$product2 = new CdProduct("My pro","Willa","Tom",5.99,5);
print "SummaryLine:{$product2->getSummaryLine()}<br/>";

$product3 = new BookProduct("My pro","Willa","Tom",5.99,10);
print "SummaryLine:{$product3->getSummaryLine()}<br/>";

点评：一般属性设置为私有的，只能通过方法来设置和获取，这样能保证安全性。