PHP面向对象继承用法详解(优化与减少代码重复)
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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