Correctly understand PHP abstract class applications

Correctly understand PHP abstract class applications_PHP tutorial

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Release： 2016-07-15 13:33:18

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In natural language, we understand that the concept of abstraction is a large description of an object, which is a description of a certain type of object. shared characteristics. The same is true in PHP. When we abstract a class, we can indicate the general behavior of the class. This class should be a template, which indicates some behaviors that its sub-methods must implement.

Definition of PHP abstract class application:

abstract class ClassName{

}

Key points of PHP abstract class application :

1. Define some methods, and subclasses must fully implement all methods in this abstraction
2. Objects cannot be created from abstract classes, their meaning is to be extended
3. Abstract classes usually have abstract methods, and there are no curly brackets in the methods

Key points for PHP abstract class application:

1. Abstract methods do not have to implement specific functions, and are determined by subclasses Completed
2. When a subclass implements a method of an abstract class, the visibility of the subclass must be greater than or equal to the definition of the abstract method
3. The method of an abstract class can have parameters or be empty
4. If the abstract method has parameters, then the implementation of the subclass must also have the same number of parameters

PHP abstract class application example:

abstract public function_name() ; //Note that there are no curly brackets

As a demonstration, let's implement a simple abstract class: calculate the area of a rectangle. This rectangle can be extended from the shape class.

<ol class="dp-xml">
<li class="alt"><span><span class="tag"><</span><span> ?PHP   </span></span></li><li><span>abstract class Shape {   </span></li><li class="alt"><span>abstract protected function get_area();   </span></li><li><span>//和一般的方法不同的是，这个方法没有大括号   </span></li><li class="alt"><span>//你不能创建这个抽象类的实例：$</span><span class="attribute">Shape_Rect<br /></span><span> = </span><span class="attribute-value">new</span><span> Shape();   </span></li><li><span>}   </span></li><li class="alt"><span>class Rectangle extends Shape{   </span></li><li><span>private $width;   </span></li><li class="alt"><span>private $height;   </span></li><li><span>function __construct($</span><span class="attribute">width</span><span>=</span><span class="attribute-value">0</span><span>,<br />$</span><span class="attribute">height</span><span>=</span><span class="attribute-value">0</span><span>){   </span></li><li class="alt"><span>$this-</span><span class="tag">></span><span class="attribute">width</span><span>=$width;   </span></span></li>
<li>
<span>$this-</span><span class="tag">></span><span class="attribute">height</span><span>=$height;   </span>
</li>
<li class="alt"><span>}   </span></li>
<li><span>function get_area(){   </span></li>
<li class="alt">
<span>echo ($this-</span><span class="tag">></span><span>width+$this-</span><span class="tag">></span><span>height)*2;   </span>
</li>
<li><span>}   </span></li>
<li class="alt"><span>}   </span></li>
<li>
<span>$</span><span class="attribute">Shape_Rect</span><span> = </span><span class="attribute-value">new</span><span> Rectangle(20,30);   </span>
</li>
<li class="alt">
<span>$Shape_Rect-</span><span class="tag">></span><span>get_area();   </span>
</li>
<li>
<span class="tag">?></span><span>   </span>
</li>
<li class="alt">
<span class="tag"><</span><span> ?PHP  </span></li><li><span>abstract class Shape {  </span></li><li class="alt"><span>abstract protected function get_area();  </span></li><li><span>//和一般的方法不同的是，这个方法没有大括号  </span></li><li class="alt"><span>//你不能创建这个抽象类的实例：$</span><span class="attribute">Shape_Rect</span><span> <br />= </span><span class="attribute-value">new</span><span> Shape();  </span></li><li><span>}  </span></li><li class="alt"><span>class Rectangle extends Shape{  </span></li><li><span>private $width;  </span></li><li class="alt"><span>private $height;  </span></li><li><span>function __construct($</span><span class="attribute">width</span><span>=</span><span class="attribute-value">0</span><span>,$</span><span class="attribute">height</span><span>=</span><span class="attribute-value">0</span><span>){  </span></li><li class="alt"><span>$this-</span><span class="tag">></span><span class="attribute">width</span><span>=$width;  </span>
</li>
<li>
<span>$this-</span><span class="tag">></span><span class="attribute">height</span><span>=$height;  </span>
</li>
<li class="alt"><span>}  </span></li>
<li><span>function get_area(){  </span></li>
<li class="alt">
<span>echo ($this-</span><span class="tag">></span><span>width+$this-</span><span class="tag">></span><span>height)*2;  </span>
</li>
<li><span>}   </span></li>
<li class="alt"><span>}  </span></li>
<li>
<span>$</span><span class="attribute">Shape_Rect</span><span> = </span><span class="attribute-value">new</span><span> Rectangle(20,30);  </span>
</li>
<li class="alt">
<span>$Shape_Rect-</span><span class="tag">></span><span>get_area();  </span>
</li>
<li>
<span class="tag">?></span><span> </span>
</li>
</ol>

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This is also a simple example, which basically illustrates the usage of abstract classes in PHP. I don’t want to say more about the rest. Personally, I think abstract classes are generally used in large projects, because I think it has too many "rules" to abide by, making it inconvenient to use! Of course this is just my opinion. I would like to say something more. PHP abstract class applications are single-inherited, which means that you can only inherit from one class, but not one class that inherits class A and class B. If you want to implement such a function, you have to use an interface. Related knowledge, I will not discuss the knowledge of PHP interface for the time being! In a word: Single inheritance and multiple interfaces!