Inheritance of object-oriented programming in PHP

Why do I need to inherit?

<?php
  Develop a set of student management system (pupil pupil, college students, ...)
  Parent class
  Class stu{
    Public $name;
    protected $age;
    protected $grade;
    Public Function Showinfo () {
       echo $this->name. "| |" $this->age;
    }
  }
  Sub Class
  Class Pupil extends stu{//pupil
    Public Function testing () {
       echo "Pupil examination";
    }
  }
  Class Graduate extends stu{//graduate student
      Public Function testing () {
       echo "Postgraduate examination";
      }
    }
Create a student
$stu 1=new pupil ();
$stu 1->testing ();
$stu 1->name= "www.bianceng.cn";
$stu 1->showinfo ();
echo "<br/>";
Create a graduate student
$stu 2=new graduate ();
$stu 2->testing ();
$stu 2->name= "Hello";
$stu 2->showinfo ();
?>

From the above code can be seen, the so-called inheritance, is a subclass by extends the parent class, the parent class Public/protect properties and methods inherited, but can not inherit the parent class private properties and methods.

Basic syntax for inheritance:

Class Name extends parent class name {

Attributes and methods required by subclasses

}

Considerations for using Inheritance:

1 subclasses can inherit the Public/protect properties and methods of the parent class, but cannot inherit the private properties and methods of the parent class.

<?php
What properties and methods of the parent class inherit from the Quilt class
Class a{
  Public $n 1=1;
  Protected $n 2= "www.bianceng.cn";
  Private $n 3=20;
  Public Function test1 () {
    echo "test1 ()";
  }
  Public Function test2 () {
    echo "Test2 ()";
  }
  Public Function test3 () {
    echo "Test3 ()";
  }
}
Class Subclass extends A{
     Function Show () {
	   echo "<br/>". $this->n2; //
	 }
  }
  Creating Subclass Objects
  $sub 1=new Subclass ();
  $sub 1->test1 ();
  echo "<br/>";
  $sub 1->test2 ();
  echo "<br/>";
$sub 1->test3 ();
echo "<br/>". $sub 1->n1;
$sub 1->show ();
?>

2 PHP inheritance is a single inheritance, that is, a subclass cannot directly inherit two parent classes

You can inherit multiple classes by inheriting the two-time method.

<?php
   Class a{
   }
   Class B extends a{
   }
   Class C extends b{//through two inheritance, C inherits A and B two classes
   }
?>

3 When the subclass object is created, the parent class's construction method is not automatically invoked by default.

<?php
Class a{
  Construction method
    Public Function __construct () {
      echo "A__construct";
     }
  }
  Class B extends a{
    function __construct () {
     echo "B__construct";
    }
  }
  Creating an Object instance
  $b =new B (); Output b__construct
?>

4 If you want to invoke the constructor or other method (public/protected) of the parent class in the subclass, you can do so (understand):

(1) Class Name:: Method Name ();

(2) Parent:: Method name ();

Cases:

<?php
Class a{
  Construction method
    Public $n 1=90;
    Public Function __construct ($n 1) {
	  $this->n1= $n 1;
      echo "A__construct";
     }
  }
  Class B extends a{
    function __construct () {
     echo "B__construct";
     Explicit method of calling the parent class
     A::__construct (900);
	 Parent::__construct (900);
    }
  }
  Creating an Object instance
  $b =new B (); Output b__construct
  echo "<br/>". $b->n1; Output 900
?>

5 if the method in the subclass (derived class) is the same as the method in the parent class (the base class), it is called a method override/method overlay.