Introduction to the use of object-oriented class inheritance in php

Inheritance of PHP classes is a relatively important knowledge point in learning the PHP language. So how do we learn PHP class inheritance correctly? In PHP object-oriented programming, class inheritance is always the most critical.

This is just like humans having children (why do we have to have children? Is it just to prevent old age! I don’t know), you take out some of your own genes and your wife’s genes. Some will regenerate into a new individual. This new personality will definitely contain the characteristics of both of you. This is an explanation of heredity (inheritance) in biology. In the world of programming, inheritance is inheritance!

First of all, after understanding some living principles of inheritance, I want to see if the inheritance of PHP classes is no longer so mysterious. Maybe it’s 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 you The "descendants" are those that possess all of your (root) characteristics. 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{
}

Description: The parent class is just an ordinary class. If you want to have descendants, you only need to add the extends keyword after the ordinary class. In this way, your subclass only has all the attributes 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 the inheritance of PHP classes 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.

<?php   
class father{   
protected $name;   
function construct($name){   
$this->name=$name;   
}   
function destruct(){   
echo "<p>{$this->name}也是要死的<br/></p>";   
}   
//这个就是所谓的构造函数，用来初始化   
function go_to_sleeping(){   
echo "<p>{$this->name}想睡觉.</p>";   
}   
function eat(){   
echo "<p>{$this->name}想吃饭.</p>";   
}   
}   
class son extends father{   
function playing(){   
//小孩子会很调皮的,当然他也是要吃要睡的生物   
echo "<p>{$this->name}正在捣蛋...</p>";   
}   
}   
$your_father=new father("老爸");   
$your_father->go_to_sleeping();   
$your_father->eat();   
$my_son=new son(&#39;宝贝&#39;);   
$my_son->go_to_sleeping();   
$my_son->eat();   
$my_son->playing();   
?>   
<?php  
class father{  
protected $name;  
function construct($name){  
$this->name=$name;  
}  
function destruct(){  
echo "<p>{$this->name}也是要死的<br/></p>";  
}  
//这个就是所谓的构造函数，用来初始化  
function go_to_sleeping(){  
echo "<p>{$this->name}想睡觉.</p>";  
}  
function eat(){  
echo "<p>{$this->name}想吃饭.</p>";  
}  
}  
class son extends father{  
function playing(){  
//小孩子会很调皮的,当然他也是要吃要睡的生物  
echo "<p>{$this->name}正在捣蛋...</p>";  
}  
}  
$your_father=new father("老爸");  
$your_father->go_to_sleeping();  
$your_father->eat();  
$my_son=new son(&#39;宝贝&#39;);  
$my_son->go_to_sleeping();  
$my_son->eat();  
$my_son->playing();  
?>

Analysis: In our first example of using inheritance, we use the constructor mentioned in the PHP constructor and the keywords in the PHP class package. If there is anything you don’t understand, just ask 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 characteristics, 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 also use the destructor to "destroy" the object, but you may not find that there are no constructors and destructors in subclasses, so The subclass inherits all the methods of the parent, otherwise how could you call $my_son->go_to_sleeping(); like this? This is the inheritance of the PHP class.

<?php
class my_class{
var $username="小鸡";
var $num=10;
function yingxiaoji(){
   //使用类里的全局变量
$num=$this->num;
$username=$this->username;
echo "我养了".$num."条".$username; 
} 
function jiegou(){
   //使用类中的函数时，用this直接引用
   $this->yingxiaoji();
   echo "全都卖了";
}
}
//php类的承 extends表示继承，但是php不允许同时继承多个基类
class my_class_extend extends my_class{
var $color="红色";
function mycolor(){
   $color=$this->color;
   $username=$this->username;
   echo ",这只".$username."是".$color;
}
}
$myname=new my_class(); //类的实例化
$myname->yingxiaoji();
echo "<br>";
//针对类中的变量重新赋值
$myname->username="小鸭子";
$myname->num="20";
$myname->yingxiaoji();
echo "<br>";
$myname->jiegou();
echo "<br>";
//初始化一个类的继承类
$myname_extend=new my_class_extend();
$myname_extend->jiegou();
$myname_extend->mycolor();
echo "<br>";
//由于是继承类，那么它的基类的属性全都有了，就可以直接给基类的变量传值
$myname_extend->username="小鸭子";
$myname_extend->num=100;
$myname_extend->color="黑色";
$myname_extend->jiegou();
$myname_extend->mycolor();
?>

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