374 lines
9.1 KiB
Markdown
374 lines
9.1 KiB
Markdown
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---
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title: Polymorphism with Abstract and Interface
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localeTitle: 具有抽象和接口的多态性
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---
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## 具有抽象和接口的多态性
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_使用Abstract类和接口与Polymorphism共享和强制执行代码_
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我们将深入研究面向对象编程,并尝试用设计模式来思考,以便使用多态来共享和实施我们的代码。
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### 抽象类
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假设我们有一个名为Man的类,它有一些属性( `name` , `age` , `height` , `fav_drinks`和`fav_sports` )和方法( `giveFirmHandshakes` , `beStubborn`和`notPutToiletPaper` )。
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```php
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<?php
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class Man
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{
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public $name;
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public $age;
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public $height;
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public $fav_sports;
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public $fav_drinks;
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public function __construct($name, $age, $height)
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{
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$this->name = $name;
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$this->age = $age;
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$this->height = $height;
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}
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public function giveFirmHandshakes()
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{
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return "I give firm handshakes.";
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}
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public function beStubborn()
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{
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return "I am stubborn.";
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}
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public function notPutToiletPaper()
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{
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return "It's not humanly possible to remember to put toilet paper rolls when they are finished";
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}
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}
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```
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我们需要指定名称,年龄和高度,以根据构造函数的要求实例化此类。
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```php
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<?php
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$jack = new Man('Jack', '26', '5 Feet 6 Inches');
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echo sprintf('%s - %s - %s', $jack->name, $jack->age, $jack->height);
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// => Jack - 26 - 5 Feet 6 Inches
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```
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现在,假设我们要为此类添加一个名为isActive的新方法。
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此方法检查属性是否处于活动状态,并根据active的值返回相应的消息,默认值为false。对于那些活跃的人,我们可以将其设置为true。
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```php
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<?php
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class Man
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{
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public $name;
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public $age;
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public $height;
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public $fav_sports;
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public $fav_drinks;
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public $active = false;
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.....
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.....
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public function isActive()
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{
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if ($this->active == true) {
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return "I am an active man.";
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} else {
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return "I am an idle man.";
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}
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}
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}
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$jack = new Man('Jack', '26', '5 Feet 6 Inches');
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$jack->active = true;
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echo $jack->isActive();
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// => I am an active man.
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$jake = new Man('Jake', '30', '6 Feet');
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echo "\n" . $jake->isActive();
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// => I am an idle man.
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```
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如果一个人不活跃或闲置怎么办?
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如果有1到4的等级来衡量一个人的活跃程度怎么办? (1 - 闲置,2 - 轻微活动,3-中等活跃,4-非常活跃)?
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我们可以有一个这样的if..elseif..else语句:
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```php
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<?php
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public function isActive()
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{
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if ($this->active == 1) {
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return "I am an idle man.";
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} elseif ($this->active == 2) {
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return "I am a lightly active man.";
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} elseif ($this->active == 3) {
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return "I am a moderately active man.";
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} else {
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return "I am a very active man.";
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}
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}
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```
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现在,让我们更进一步。
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如果Man的活动属性不仅仅是一个整数(1,2,3,4等)怎么办?
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如果活跃的价值是“运动”或“懒惰”怎么办?
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我们不是必须添加更多的elseif语句来寻找与这些字符串的匹配吗?
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抽象类可用于此类场景。
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对于抽象类,您基本上将类定义为抽象,并将要强制实现的方法定义为抽象,而不实际将任何代码放在这些方法中。
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然后创建一个扩展父抽象类的子类,并在该子类中实现抽象方法。
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这样,您将强制执行所有子类以定义自己的抽象方法版本。让我们看看如何将`isActive()`方法设置为抽象。
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# 1:将类定义为抽象。
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```php
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<?php
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abstract class Man
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{
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.....
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.....
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}
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```
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# 2:为要在抽象类中强制执行的方法创建抽象方法。
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```php
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<?php
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abstract class Man
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{
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.....
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.....
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abstract public function isActive();
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}
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```
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# 3:创建扩展抽象类的子类。
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```php
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<?php
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class AthleticMan extends Man
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{
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.....
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.....
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}
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```
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# 4:在子类中实现抽象方法。
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```php
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<?php
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class AthleticMan extends Man
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{
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public function isActive()
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{
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return "I am a very active athlete.";
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}
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}
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```
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# 5:实例化子类(不是抽象类)。
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```php
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<?php
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$jack = new AthleticMan('Jack', '26', '5 feet 6 inches');
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echo $jack->isActive();
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// => I am a very active athlete.
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```
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完整的抽象类定义和实现代码:
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```php
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<?php
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abstract class Man
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{
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public $name;
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public $age;
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public $height;
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public $fav_sports;
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public $fav_drinks;
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public function __construct($name, $age, $height)
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{
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$this->name = $name;
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$this->age = $age;
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$this->height = $height;
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}
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public function giveFirmHandshakes()
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{
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return "I give firm handshakes.";
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}
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public function beStubborn()
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{
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return "I am stubborn.";
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}
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public function notPutToiletPaper()
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{
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return "It's not humanly possible to remember to put toilet paper rolls when they are finished";
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}
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abstract public function isActive();
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}
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class AthleticMan extends Man
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{
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public function isActive()
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{
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return "I am a very active athlete.";
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}
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}
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$jack = new AthleticMan('Jack', '26', '5 feet 6 inches');
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echo $jack->isActive();
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// => I am a very active athlete.
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```
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在这段代码中,您会注意到`isActive()`抽象方法是在`Man`抽象类中定义的,它是在子类`AthleticMan` 。
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现在`Man`类无法直接实例化来创建对象。
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```php
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<?php
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$ted = new Man('Ted', '30', '6 feet');
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echo $ted->isActive();
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// => Fatal error: Uncaught Error: Cannot instantiate abstract class Man
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```
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此外,抽象类( `Man`类)的每个子类都需要实现所有抽象方法。缺乏此类实施将导致致命错误。
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```php
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<?php
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class LazyMan extends Man
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{
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}
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$robert = new LazyMan('Robert', '40', '5 feet 10 inches');
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echo $robert->isActive();
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// => Fatal error: Class LazyMan contains 1 abstract method
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// => and must therefore be declared abstract or implement
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// => the remaining methods (Man::isActive)
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```
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通过使用抽象类,您可以强制某些方法由子类单独实现。
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### 接口
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还有另一种面向对象的编程概念,它与名为Interface的抽象类密切相关。
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抽象类和接口之间的唯一区别在于,在抽象类中,您可以在父类中混合使用已定义的方法( `giveFirmHandshakes()` , `isStubborn()`等)和抽象方法( `isActive()` ),而在接口中,你只能在父类中定义(而不是实现)方法。
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让我们看看如何将Man抽象类转换为接口。
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# 1:使用所有方法定义接口(使用接口而不是类)。
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```php
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<?php
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interface Man
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{
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public function __construct($name, $age, $height);
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public function giveFirmHandshakes();
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public function beStubborn();
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public function notPutToiletPaper();
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public function isActive();
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}
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```
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# 2:创建一个实现接口的类(使用implements而不是extends)。该类必须实现接口内定义的所有方法,包括构造方法。
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```php
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<?php
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class AthleticMan implements Man
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{
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public $name;
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public $age;
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public $height;
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public function __construct($name, $age, $height)
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{
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$this->name = $name;
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$this->age = $age;
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$this->height = $height;
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}
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public function giveFirmHandshakes()
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{
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return "I give firm handshakes.";
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}
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public function beStubborn()
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{
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return "I am stubborn.";
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}
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public function notPutToiletPaper()
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{
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return "It's not humanly possible to remember to put toilet paper rolls when they are finished";
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}
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public function isActive()
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{
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return "I am a very active athlete.";
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}
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}
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```
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# 3:实例化实施班(AthleticMan)
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```php
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<?php
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$jack = new AthleticMan('Jack', '26', '5 feet 6 inches');
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echo $jack->isActive();
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// => I am a very active athlete.
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```
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使用接口,您需要记住:
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* 这些方法无法在界面内实现。
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* 无法在界面内定义变量(属性)。
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* 接口内定义的所有方法都需要在子(实现)类中实现。
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* 需要在子类中定义所有必需的变量。
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* Man接口强制实现其实现类以实现接口中的所有方法。
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那么,接口的用途是什么?
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难道我们不能只创建一个新类AthleticMan并创建所有方法而不是实现接口吗?
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这就是_设计模式_发挥作用的地方。
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当有一个基类( `Man` )想要强制你做某事时(构造一个对象,给定一个握手,beStubborn,notPutToiletPaper并检查你是否活跃)但是不想告诉你具体如何去做,就会使用接口。
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您可以继续使用您认为合适的实现来创建实现类。
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只要实现了所有方法, `Man`接口就不关心如何了。
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我们已经了解了如何以及何时在PHP中使用抽象类和接口。使用这些OOP概念使具有不同功能的类共享相同的基础“蓝图”(抽象类或接口)称为多态。
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