Summary of examples of PHP related knowledge points

The examples in this article summarize the relevant knowledge points of PHP class. Share it with everyone for your reference, the details are as follows:

Final class and final method

If the method in the parent class is declared as final, the subclass cannot override the method. If a class is declared final, it cannot be inherited.

final class a{}
class a{
  final public function A(){}
}

Abstract classes and abstract methods

abstract class a {
  public abstract function func();
}
class A extends a{
  public function func(){}
}

① A class can be declared as an abstract class using abstract; an abstract class is a class that cannot be instantiated and is only used as a parent class for other classes.

abstract class name{}

② A method can be declared as an abstract method using abstract; abstract methods only need to declare the method header and do not need the method body in the braces.

abstract public function name($val);

③ If there is an abstract method in a class, the class must be declared as an abstract class.

④ If a subclass inherits from an abstract class, the subclass cannot implement all abstract methods in the parent class unless the subclass also continues to be an abstract class.

⑤ When a subclass implements a method of an abstract parent class, the access control scope cannot be reduced, and the method parameters must also be consistent (rewritten).

Interface

Interface can be regarded as a higher level abstraction of abstract class, it can be said to be a special case of abstract class

interface a{
  function func();
}
class A implements a {
  function func(){}
}

Class: attributes, class constants, methods

Abstract class: attributes, class constants , Abstract methods

Interface: interface constants, abstract methods

① Compared with abstract classes, interfaces can implement 'multiple inheritance'

class A implements a,b,c{}

② An interface can only inherit one interface

interface a extends b{}

③ The methods are all abstract methods without abstract modification, that is, the lower-level classes either implement the interface methods (implements) or are also declared as abstract methods

Overloading technology

1. Attribute overloading: If you use a non-existent attribute, then A predefined method in the class will be called to process data;

For application scenarios where attributes are not used, the following processing is done

① Value: Automatically call __get() in the class
② Assignment: Automatically call __get() in the class __set()
③ Determine whether it exists: automatically call __isset()
④ in the class Destruction: automatically call __unset() in the class

The premise is that these methods are pre-defined, otherwise an error will be reported

<?php
class bee{
  public $ol = array();
  public function __get($key){
    if(isset($this->ol[$key])){
      return $this->ol[$key];
    }
    return $key.&#39; not exists&#39;;
  }
  public function __set($key,$val){
    $this->ol[$key] = $val;
  }
  public function __isset($key){
    if(isset($this->ol[$key])){
      return true;
    }
    return false;
  }
  public function __unset($key){
    unset($this->ol[$key]);
  }
}
$obj = new bee();
echo $obj->one;
echo &#39;<br>&#39;;
$obj->one = 1;
echo $obj->one;
echo &#39;<br>&#39;;
var_dump(isset($obj->one));

The running results are as follows:

one not exists
1
boolean true

2. Method overloading: If a method that does not exist is used, a predefined method in the class will be called to handle the behavior;

It is not used for methods For application scenarios, do the following processing

① Call inaccessible methods in objects: __call()
② Call inaccessible methods in static mode: __callStatic()

<?php
class bee{
  public function __call($name,$arr){
    echo &#39;<br>&#39;;
    echo &#39;function &#39;.$name.&#39; not exist&#39;;
  }
  static function __callStatic($name,$arr){
    echo &#39;<br>&#39;;
    echo &#39;function &#39;.$name.&#39; not exist&#39;;
  }
  /*public function __call($name,$arr){
    $num = count($arr);
    if($num<1){
      $name();
    }else{
      $name = $name.&#39;_one&#39;;
      $name($arr[0]);
    }
  }*/
}
$obj->func();
bee::staFunc();
/*$obj->func(1);
function func(){
  echo &#39;<br>&#39;;
  echo &#39;no.0&#39;;
}
function func_one($val){
  echo &#39;<br>&#39;;
  echo &#39;no.&#39;.$val;
}*/

The running results are as follows:

function func not exist
function staFunc not exist

Note: The above methods are all magic methods with parameters

I hope this article will be helpful to everyone in PHP programming.