本文实例讲述了php面向对象继承用法。分享给大家供大家参考，具体如下：
继承
先看两个类
<?php
class cdproduct {
public $playlength; // 播放时间
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; // 看的页数
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 getnumberofpages() {
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}";
}
}
$product1 = new cdproduct("cd1", "bob", "bobbleson", 4, 50 );
print $product1->getsummaryline();
print "n";
$product2 = new bookproduct("book1", "harry", "harrelson", 4, 30 );
print $product2->getsummaryline();
print "n";
?>
输出：
cd1 ( bobbleson, bob ): playing time - 50
book1 ( harrelson, harry ): page count - 30
点评：这两个类，代码重复性太高，有相同性，也有差异性。不如用继承来简化处理。
采用继承来处理
<?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() { // 增加属于自己的方法
return $this->playlength;
}
function getsummaryline() { // 改造了父类的方法
$base = "{$this->title} ( {$this->producermainname}, ";
$base .= "{$this->producerfirstname} )";
$base .= ": playing time - {$this->playlength}";
return $base;
}
}
class bookproduct extends shopproduct {
function getnumberofpages() {
return $this->numpages;
}
function getsummaryline() {
$base = "{$this->title} ( {$this->producermainname}, ";
$base .= "{$this->producerfirstname} )";
$base .= ": page count - {$this->numpages}";
return $base;
}
}
$product1 = new cdproduct("cd1", "bob", "bobbleson", 4, null, 50 );
print $product1->getsummaryline();
print "n";
$product2 = new bookproduct("book1", "harry", "harrelson", 4, 30 );
print $product2->getsummaryline();
print "n";
?>
输出：
cd1 ( bobbleson, bob ): playing time - 50
book1 ( harrelson, harry ): page count - 30
点评：继承处理很好的解决了差异性，相通性问题。
进一步优化处理
<?php
class shopproduct {
// 抽离出共有属性
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 {
// 抽离出属于自己特有的属性
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; // 处理自己专有的属性
}
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 getnumberofpages() {
return $this->numpages;
}
function getsummaryline() {
$base = "$this->title ( $this->producermainname, ";
$base .= "$this->producerfirstname )";
$base .= ": page count - $this->numpages";
return $base;
}
}
$product1 = new cdproduct("cd1", "bob", "bobbleson", 4, 50 );
print $product1->getsummaryline();
print "n";
$product2 = new bookproduct("book1", "harry", "harrelson", 4, 30 );
print $product2->getsummaryline();
print "n";
?>
输出：
cd1 ( bobbleson, bob ): playing time - 50
book1 ( harrelson, harry ): page count - 30
点评：这里把共有属性在父类中，其他个性属性放在自己的类中处理。并设置自己的构造方法，继承父类的构造方法。
进一步继承父类的方法
<?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 );
$this->playlength = $playlength;
}
function getplaylength() {
return $this->playlength;
}
function getsummaryline() {
$base = parent::getsummaryline();
$base .= ": playing time - {$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 getnumberofpages() {
return $this->numpages;
}
function getsummaryline() {
$base = parent::getsummaryline();
$base .= ": page count - {$this->numpages}";
return $base;
}
}
$product1 = new cdproduct("cd1", "bob", "bobbleson", 4, 50 );
print $product1->getsummaryline();
print "n";
$product2 = new bookproduct("book1", "harry", "harrelson", 4, 30 );
print $product2->getsummaryline();
print "n";
?>
输出：
cd1 ( bobbleson, bob ): playing time - 50
book1 ( harrelson, harry ): page count - 30
点评：同样的结果，可以优化优化再优化。这里继承父类的方法。parent::getsummaryline()。不过这个用的比较少。
继续添加一些有意思的内容
<?php
class shopproduct {
private $title;
private $discount = 0;
private $producermainname;
private $producerfirstname;
protected $price;
function __construct( $title, $firstname,
$mainname, $price ) {
$this->title = $title;
$this->producerfirstname = $firstname;
$this->producermainname = $mainname;
$this->price = $price;
}
function setdiscount( $num ) {
$this->discount=$num;
}
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 {
public $playlength;
function __construct( $title, $firstname,
$mainname, $price, $playlength ) {
parent::__construct( $title, $firstname,
$mainname, $price );
$this->playlength = $playlength;
}
function getplaylength() {
return $this->playlength;
}
function getsummaryline() {
$base = parent::getsummaryline();
$base .= ": playing time - {$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 getprice() {
return $this->price;
}
function getnumberofpages() {
return $this->numpages;
}
function getsummaryline() {
$base = parent::getsummaryline();
$base .= ": page count - {$this->numpages}";
return $base;
}
}
$product1 = new cdproduct("cd1", "bob", "bobbleson", 4, 50 );
$product1->setdiscount( 3 );
print $product1->getsummaryline();
print "n";
print "price: {$product1->getprice()}n";
$product2 = new bookproduct("book1", "harry", "harrelson", 4, 30 );
$product2->setdiscount( 3 ); // 折扣对book无效
print $product2->getsummaryline();
print "n";
print "price: {$product2->getprice()}n";
?>
输出：
cd1 ( bobbleson, bob ): playing time - 50
price: 1
book1 ( harrelson, harry ): page count - 30
price: 4
点评:父类添加了折扣，book继承之后，修改了getprice方法，所以折扣对book无效。
私有化属性，通过方法来设置与获取
<?php
class shopproduct {
// 私有化属性，通过方法来设置与获取
private $title;
private $producermainname;
private $producerfirstname;
protected $price;
private $discount = 0;
public 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 - $this->discount);
}
public function getproducer() {
return "{$this->producerfirstname}".
" {$this->producermainname}";
}
public function getsummaryline() {
$base = "{$this->title} ( {$this->producermainname}, ";
$base .= "{$this->producerfirstname} )";
return $base;
}
}
class cdproduct extends shopproduct {
private $playlength = 0;
public function __construct( $title, $firstname,
$mainname, $price, $playlength ) {
parent::__construct( $title, $firstname,
$mainname, $price );
$this->playlength = $playlength;
}
public function getplaylength() {
return $this->playlength;
}
public function getsummaryline() {
$base = parent::getsummaryline();
$base .= ": playing time - {$this->playlength}";
return $base;
}
}
class bookproduct extends shopproduct {
private $numpages = 0;
public function __construct( $title, $firstname,
$mainname, $price, $numpages ) {
parent::__construct( $title, $firstname,
$mainname, $price );
$this->numpages = $numpages;
}
public function getnumberofpages() {
return $this->numpages;
}
public function getsummaryline() {
$base = parent::getsummaryline();
$base .= ": page count - {$this->numpages}";
return $base;
}
public function getprice() {
return $this->price;
}
}
$product1 = new cdproduct("cd1", "bob", "bobbleson", 4, 50 );
print $product1->getsummaryline()."n";
$product2 = new bookproduct("book1", "harry", "harrelson", 4, 30 );
print $product2->getsummaryline()."n";
?>
输出：
cd1 ( bobbleson, bob ): playing time - 50
book1 ( harrelson, harry ): page count - 30
点评：这里进一步私有化了属性，要想获取只能通过方法。这样就确保了安全性。
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