In the last basic article, K introduced you to the use of arrays and strings in PHP. This time, K decided to give it a one-time release and share with you the object-oriented methods in PHP. Three major features: knowledge in three aspects: encapsulation, inheritance, and polymorphism.

1. Encapsulation

In PHP, encapsulation can be summarized in three sub-sections: privatization. Specifically, access control is achieved by privatizing properties and methods in the class that do not require external access through access modifiers.

So what is the function of encapsulation? There are two main functions of encapsulation. One is method encapsulation, which exposes the functions that users care about and hides functions that other users cannot use; the other is property encapsulation, that is Control user data to prevent illegal data transmission settings.

So how is the encapsulation operation implemented?

For method encapsulation, we set it by adding the private keyword before the method, that is, privatization. The demo is as follows:

private function formatName(){} // 这个方法仅仅能在类内部使用$this调用 function showName(){             $this -> formatName();
         }

For attribute encapsulation, we can implement it in two ways.

First, set/read privatized properties through the set/get methods provided by itself. The demo is as follows:

private $age;         function setAge($age){             $this -> age = $age;
         }         function getAge(){             return $this -> age;
         }

　The second isimplemented through magic methods. The demo is as follows:

private $age;function __get($key){return $this -> $key;
}function __set($key,$value){$this -> $key = $value;
}$对象 -> age;  >>> 访问对象私有属性时，自动调用__get()魔术方法，并且将访问的属性名传给__get()方法；$对象 -> age = "11";  >>> 设置对象的私有属性时，自动调用__set()魔术方法，并且将设置的属性名以及属性值传给__set()方法；

　In addition, the magic methods related to encapsulation mainly include the following:

　 ① __set( ): Automatically called when assigning values ​​to class private attributes. When calling, pass two parameters to the object, the attribute name and attribute value that need to be set
　 ② __get(): Automatically called when reading class private attributes , pass a parameter to the method when calling, the attribute name that needs to be read
③ __isset(): Automatically called when the isset() function is used externally to detect private attributes.
　>>> Use isset() outside the class to detect private attributes, which are not detected by default. That is false
　　>>>So, we can use the __isset() function to return the internal detection result when automatically called.
Function __isset($key){
Return isset($this->$key);
}
When external isset($object name->private attribute) is used for detection, the result returned by the above __isset() will be automatically called!
　 ④ __unset(): Automatically called when the unset() function is used externally to delete private attributes.
Function __unset($key){
unset($this->$key);
}
When an attribute is deleted externally using unset($object name->private attribute), the attribute name is automatically passed to __unset() and handed over to this magic method for processing.

2. Inheritance

## In PHP, inheritance can also use the word extends to summarize. Extends is used on a subclass to allow the subclass to inherit non-private properties and methods from the parent class. The demo is as follows:

class Student extends Person{}

parent::方法名();

function __construct($name,$age,$school){
    parent::__construct($name,$age);$this -> school = $school;
}// 其中name、age属性继承自父类，school属于子类

    abstract class Person{abstract function say();
    }    class Chinese extends Person{ // 条件一：子类继承父类function say(){ // 条件二：子类重写父类方法echo "我说中文！<br>";
        }
    }class English extends Person{ //条件一：子类继承父类function say(){ // 条件二：子类重写父类方法echo "I speak English!<br>";            
        }
    }    
//    Person $c = new Chinese(); // 父类引用指向子类对象，PHP中此形式行不通
//    Person $e = new English();function func(Person $p){ //PHP中的类型约束只存在与函数的形参$p -> say();
    }
    func(new Chinese()); // 条件三：父类引用指向子类对象func(new English()); // 条件三：父类引用指向子类对象

The above is the detailed content of Preliminary understanding of PHP - encapsulation, inheritance, polymorphic features. For more information, please follow other related articles on the PHP Chinese website!