Three aspects of life in object-oriented php

In object-oriented thinking, there are three major characteristics: Encapsulation, Inheritance and Polymorphism.

1. Encapsulation

a. Definition: Encapsulation, literally means to put the content into a container , and be sealed and stored. In the Object-oriented idea, encapsulation refers to bundling data and operations on the data to hide it from the outside world while providing an operable interface to the outside world. Similar to the power adapter of a mobile phone, you only need to put both ends of the plug into the socket and power cord, regardless of how the power adapter converts the 220v voltage into a voltage that the mobile phone can support.

b. Example

//封装特性
class Salary{				//将数据和方法都放置进类内部，不可见
    private static $count = 0;
    private $money = 0;		 
    
    public function getMoney(){			//对类内的数据进行操作
        return $this->money;
    }  
}

//类外部
$s = new Salary();
$s->getMoney();				//外部只能访问类中公有的方法，具体实现不可见

2. Inheritance

a.Definition: Inheritance, literally means that a son inherits from his father The son strives based on the foundation laid by his father. In object-oriented programming, we call the empire built by the father parentclass, and the empire inherited by the son from his father is called subclass.

b. Example

<?php
  class Fu{}
  class Zi extends Fu{} //利用关键字extends表示Zi类是Fu类的子类。
?>

3. Polymorphism

a. Definition: Polymorphism means that when class inheritance occurs, method override ## occurs at the same time #, that is, subclass has a method with the same name as parent class . Then when instantiating the object, let the parent class object point to the subclass object (mandatory type, PHP is a weakly typed language does not support), and the parent class object expresses the characteristics of the subclass object.

b. Example (Polymorphism requires a strongly typed language, so you can take

Java as an example)

//父类
class Animal{
    public void show(){
         System.out.println("Animal");//这是打印Animal然后换行
    }
}

//子类
class Dog extends Father{
    //重写show方法
    public void show(){
         System.out.println("Dog");//这是打印Dog然后换行
    }
}

//实例化：Java是强类型，必须指定保存数据的变量的类型
Animal a = new Dog();	 //父类对象指向子类对象空间
a.show();				//打印Dog，父类对象调用的是子类方法

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