What are inheritance and derivation in PHP? How do we use inheritance?

The previous article introduced you to "How to use the constructor and this keyword in PHP? How to introduce constructor? 》, this article continues to introduce to you what inheritance and derivation are in PHP? How do we use inheritance? It has certain reference value. Friends in need can refer to it. I hope it will be helpful to everyone.

Inheritance

1. Basic concepts

Inheritance and derivation

are actually the same concept, but they are understood from different perspectives. If understood from the same attributes, the above relationship is called inheritance. If understood from unique attributes, the above relationship is called derivation.

Name of parent and child classes

Parent class==Subclass

Base class==Derived class

Single inheritance

Subclasses can only have one parent class

We create a new file, first we write a class, (class, animal), then define attributes and methods in it, and then we write a Class, (class, perso), then how do we use person to inherit animal? We can add a space after person, write extends, and then write the parent class name after it,

Let’s take the code as an example:

<?php
class Animal
{
    public $name;
    public function pome()
{
    echo &#39; 我喜欢你&#39;;
}
}
class Person extends Animal
{
}

2. Inheritance syntax

Basic syntax

extends :继承
格式:
class Tidy extends Dog{ }

If a subclass inherits the parent class, then it will have the attributes of the parent class. and methods.

The subclass has all the attributes of the parent class, as well as its own unique attributes

For the above sentence, let’s verify it,

We still According to the above code, we give a value in Animal, and then define a new object in person. Let’s take the code as an example:

<?php
class Animal
{
    public $name = &#39;林徽因:&#39;;
    public function pome()
{
    echo &#39;答案很长,我准备用一生的时间来回答,你准备要听了吗?&#39;;
}
}
class Person extends Animal
{
}
$xiaoming = new Person() ;
echo $xiaoming ->name ;
$xiaoming->pome();

The running results are as follows:

Access permissions

public                                                                                                                                                                       External, only public can be directly accessed

Both public and protected can be inherited by subclasses

private cannot be inherited by subclasses

External access Subclass Inherit

public                                           over                                                           use   use                   use   use   use                 use   use   –                                                                   # The modification function is the same

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