The use of class inheritance in PHP object-oriented_PHP tutorial

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 some of your wife’s genes, and regenerate To become 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 would like 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 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 a "root" class (parent class or base class)

Syntax: class father{

}

1. Generate "descendants" (subclasses)

Syntax: class son extends father{

}

Note: 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 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.
class father{
protected $name;
function __construct($name){
$this->name=$name;
}
function __destruct(){
echo "

{$this->name} is also going to die

";
}
//This is the so-called constructor, used to initialize
function go_to_sleeping(){
echo "

{$this->name} wants to sleep.

";
}
function eat(){
echo "

{$this->name} wants to eat.

";
}
}
class son extends father{
function playing(){
//Children can be very naughty, and of course they are creatures that need to eat and sleep
echo "

{$this->name} is causing trouble...

";
}
}
$your_father=new father("Dad");
$your_father->go_to_sleeping();
$your_father->eat();
$my_son=new son(baby);
$my_son->go_to_sleeping();
$my_son->eat();
$my_son->playing();
?>
class father{
protected $name;
function __construct($name){
$this->name=$name;
}
function __destruct(){
echo "

{$this->name} is also going to die

";
}
//This is the so-called constructor, used for initialization
function go_to_sleeping(){
echo "

{$this->name} wants to sleep.

";
}
function eat(){
echo "

{$this->name} wants to eat.

";
}
}
class son extends father{
function playing(){
//Children can be very naughty, and of course they are creatures that need to eat and sleep
echo "

{$this->name} is causing trouble...

";
}
}
$your_father=new father("Dad");
$your_father->go_to_sleeping();
$your_father->eat();
$my_son=new son(baby);
$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 encapsulation. If there is anything you don’t understand, go take a look! 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, people are related to 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.

The article is quoted from: http://club.topsage.com/thread-501298-1-1.html

class my_class{
var $username="Chicken";
var $num=10;
function yingxiaoji(){
//Use global variables in the class
$num=$this->num;
$username=$this->username;
echo "I have raised".$num." Articles".$username;
}
function jiegou(){
//When using functions in a class, use this to directly reference
$this->yingxiaoji();
echo "All sold";
}
}
//Inheritance of php class extends means inheritance, but php does not allow inheritance of multiple base classes at the same time
class my_class_extend extends my_class{

var $color="red";
function mycolor(){
$color=$this->color;
$username=$this->username;
echo ",This ".$username." is ".$color;
}
}
$myname=new my_class(); //Instantiation of class
$myname->yingxiaoji();
echo "
";

//Reassign the variables in the class
$myname->username="Little Duck";
$myname->num="20";
$myname->yingxiaoji();
echo "
";

$myname->jiegou();
echo "
";

//Initialize the inherited class of a class
$myname_extend=new my_class_extend();
$myname_extend->jiegou();
$myname_extend->mycolor();

echo "
";
//Since it is an inherited class, it has all the attributes of its base class, and you can directly pass values ​​to the variables of the base class
$myname_extend->username="Little Duck";
$myname_extend->num=100;
$myname_extend->color="black";
$myname_extend->jiegou();
$myname_extend->mycolor();
?>