A Deep Dive into Inheritance of PHP Classes_PHP Tutorial-PHP Tutorial-php.cn

This is just like humans having children (why must they have children? Is it just to prevent old age! I don’t know), you put Take some of your own genes and some of your wife's genes to create a new individual. This new personality will definitely contain the characteristics of both of you. This is a biological explanation of heredity (inheritance). In the world of programming, inheritance is inheritance!

First of all, after understanding some living principles of inheritance, I would like to see if the inheritance of PHP classes is no longer so mysterious. Perhaps it is not mysterious in the first place because we ourselves are too complicated. In order to have inheritance, there must be a "root". For this "root", you may imagine that if you give birth to a son or daughter in the future, they will get some "things (properties and methods)" from you, so that your "descendants" will continue to inherit. Has all the characteristics of your (roots). Let's describe how this is expressed in PHP's object-oriented language through grammar (it can't be as direct as humans, get married, and your offspring will be produced after a while)

1. Generate "roots" Class (parent class or base class)

Syntax: class father{

}

1. Generate "descendants" (subclasses)

Syntax: class son extends father{

}

Explanation: The parent class is just an ordinary class. If you want to have descendants, you only need to add it to the ordinary class Just add the extends keyword at the end, so that your subclass only has all the properties and methods of the parent class. It's actually that simple.

Let’s do something practical. After all, defining a parent class and subclass in PHP class inheritance is to complete a certain task! The task here is relatively monotonous. Take people as an example. People have names (attributes) and they have to sleep and eat (methods). Let's use this basic task to complete the knowledge in this section.

<ol class="dp-xml">
<li class="alt"><span><span class="tag"><</span><span> ?php   </span></span></li><li><span>class father{   </span></li><li class="alt"><span>protected $name;   </span></li><li><span>function __construct($name){   </span></li><li class="alt"><span>$this-</span><span class="tag">></span><span class="attribute">name</span><span>=$name;   </span></span></li>
<li><span>}   </span></li>
<li class="alt"><span>function __destruct(){   </span></li>
<li>
<span>echo "</span><span class="tag"><</span><span> </span><span class="tag-name">p</span><span class="tag">></span><span>{$this-</span><span class="tag">></span><span>name}也是要死的</span><span class="tag"><</span><span> </span><span class="tag-name">br</span><span class="tag">/></span><span class="tag"><</span><span> /p</span><span class="tag">></span><span>";   </span>
</li>
<li class="alt"><span>}   </span></li>
<li><span>//这个就是所谓的构造函数，用来初始化   </span></li>
<li class="alt"><span>function go_to_sleeping(){   </span></li>
<li>
<span>echo "</span><span class="tag"><</span><span> </span><span class="tag-name">p</span><span class="tag">></span><span>{$this-</span><span class="tag">></span><span>name}想睡觉.</span><span class="tag"><</span><span> /p</span><span class="tag">></span><span>";   </span>
</li>
<li class="alt"><span>}   </span></li>
<li><span>function eat(){   </span></li>
<li class="alt">
<span>echo "</span><span class="tag"><</span><span> </span><span class="tag-name">p</span><span class="tag">></span><span>{$this-</span><span class="tag">></span><span>name}想吃饭.</span><span class="tag"><</span><span> /p</span><span class="tag">></span><span>";   </span>
</li>
<li><span>}   </span></li>
<li class="alt"><span>}   </span></li>
<li><span>class son extends father{   </span></li>
<li class="alt"><span>function playing(){   </span></li>
<li><span>//小孩子会很调皮的,当然他也是要吃要睡的生物   </span></li>
<li class="alt">
<span>echo "</span><span class="tag"><</span><span> </span><span class="tag-name">p</span><span class="tag">></span><span>{$this-</span><span class="tag">></span><span>name}正在捣蛋...</span><span class="tag"><</span><span> /p</span><span class="tag">></span><span>";   </span>
</li>
<li><span>}   </span></li>
<li class="alt"><span>}   </span></li>
<li>
<span>$</span><span class="attribute">your_father</span><span>=</span><span class="attribute-value">new</span><span> father("老爸");   </span>
</li>
<li class="alt">
<span>$your_father-</span><span class="tag">></span><span>go_to_sleeping();   </span>
</li>
<li>
<span>$your_father-</span><span class="tag">></span><span>eat();   </span>
</li>
<li class="alt">
<span>$</span><span class="attribute">my_son</span><span>=</span><span class="attribute-value">new</span><span> son('宝贝');   </span>
</li>
<li>
<span>$my_son-</span><span class="tag">></span><span>go_to_sleeping();   </span>
</li>
<li class="alt">
<span>$my_son-</span><span class="tag">></span><span>eat();   </span>
</li>
<li>
<span>$my_son-</span><span class="tag">></span><span>playing();   </span>
</li>
<li class="alt">
<span class="tag">?></span><span>   </span>
</li>
<li>
<span class="tag"><</span><span> ?php  </span></li><li class="alt"><span>class father{  </span></li><li><span>protected $name;  </span></li><li class="alt"><span>function __construct($name){  </span></li><li><span>$this-</span><span class="tag">></span><span class="attribute">name</span><span>=$name;  </span>
</li>
<li class="alt"><span>}  </span></li>
<li><span>function __destruct(){  </span></li>
<li class="alt">
<span>echo "</span><span class="tag"><</span><span> </span><span class="tag-name">p</span><span class="tag">></span><span>{$this-</span><span class="tag">></span><span>name}也是要死的</span><span class="tag"><</span><span> </span><span class="tag-name">br</span><span class="tag">/></span><span class="tag"><</span><span> /p</span><span class="tag">></span><span>";  </span>
</li>
<li><span>}  </span></li>
<li class="alt"><span>//这个就是所谓的构造函数，用来初始化  </span></li>
<li><span>function go_to_sleeping(){  </span></li>
<li class="alt">
<span>echo "</span><span class="tag"><</span><span> </span><span class="tag-name">p</span><span class="tag">></span><span>{$this-</span><span class="tag">></span><span>name}想睡觉.</span><span class="tag"><</span><span> /p</span><span class="tag">></span><span>";  </span>
</li>
<li><span>}  </span></li>
<li class="alt"><span>function eat(){  </span></li>
<li>
<span>echo "</span><span class="tag"><</span><span class="tag-name">p</span><span class="tag">></span><span>{$this-</span><span class="tag">></span><span>name}想吃饭.</span><span class="tag"></</span><span class="tag-name">p</span><span class="tag">></span><span>";  </span>
</li>
<li class="alt"><span>}  </span></li>
<li><span>}  </span></li>
<li class="alt"><span>class son extends father{  </span></li>
<li><span>function playing(){  </span></li>
<li class="alt"><span>//小孩子会很调皮的,当然他也是要吃要睡的生物  </span></li>
<li>
<span>echo "</span><span class="tag"><</span><span> </span><span class="tag-name">p</span><span class="tag">></span><span>{$this-</span><span class="tag">></span><span>name}正在捣蛋...</span><span class="tag"><</span><span> /p</span><span class="tag">></span><span>";  </span>
</li>
<li class="alt"><span>}  </span></li>
<li><span>}  </span></li>
<li class="alt">
<span>$</span><span class="attribute">your_father</span><span>=</span><span class="attribute-value">new</span><span> father("老爸");  </span>
</li>
<li>
<span>$your_father-</span><span class="tag">></span><span>go_to_sleeping();  </span>
</li>
<li class="alt">
<span>$your_father-</span><span class="tag">></span><span>eat();  </span>
</li>
<li>
<span>$</span><span class="attribute">my_son</span><span>=</span><span class="attribute-value">new</span><span> son('宝贝');  </span>
</li>
<li class="alt">
<span>$my_son-</span><span class="tag">></span><span>go_to_sleeping();  </span>
</li>
<li>
<span>$my_son-</span><span class="tag">></span><span>eat();  </span>
</li>
<li class="alt">
<span>$my_son-</span><span class="tag">></span><span>playing();  </span>
</li>
<li>
<span class="tag">?></span><span> </span>
</li>
</ol>

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Analysis: In our first example of using inheritance, we use the constructor mentioned in the PHP constructor and the keywords in the PHP class encapsulation. If you don’t understand anything, Go check it out! I don’t want to say any more. I didn’t want to sleep at noon. Let’s talk about this little program.

In the father of the class, we define general features, such as the person’s name, what the person needs to eat and sleep, and then in its subclass (descendant) we define a personalized method (playing), After all, there are differences between people. We use the constructor to initialize the name, and of course we use the destructor to "destroy" the object. But you may not find that there are no constructors and destructors in the subclass, so the subclass inherits the parent All methods, otherwise how can you call $my_son->go_to_sleeping(); like this? This is the inheritance of the PHP class.