Detailed explanation of the definition and rule usage of abstract classes and abstract methods in PHP

In Object-oriented (OOP) language, a class can have one or more subclasses, and each class has at least one public method as external code Access interface. Abstract methods are introduced to facilitate inheritance. Now let’s take a look at how abstract classes and abstract methods are defined respectively and their characteristics.

What is an abstract method? The method we define in the class with only the method name and no method body is an abstract method. The so-called no method body means that when the method is declared, there is no curly brackets and its contents. Instead, when it is declared directly, a semicolon is added after the method name. , In addition, when declaring an abstract method, add a keyword "abstract" to modify it.

1. Abstract keyword: abstract

Abstract means that it cannot be explained exactly, but it has a certain concept or name. To declare an abstract class or method in PHP, we need to use the abstract keyword. .

2. Definition of abstract methods and abstract classes

If at least one method in a class is abstract, we call it an abstract class. So if you define an abstract class, first define the abstract method.

The code is as follows:

abstract class class1{                                            
   abstract function fun1(); 
   ……
}

1. There is at least one abstract method in the class
2. Abstract methods are not allowed to have { }
3. The abstract method must be preceded by Add abstract

3. Rules for using abstract classes and methods

Several characteristics of abstract classes:

1. They cannot be instantiated, only Inherited

2. In the inherited derived class, all abstract methods must be overloaded before they can be instantiated

The statement about abstract methods is as follows:

The code is as follows:

<?php
abstract function fun1();
?>

What is an abstract class? As long as a method in a class is an abstract method, then the class must be defined as an abstract class. Abstract classes must also be modified with the keyword "abstract". Abstract classes cannot instantiate objects, so abstract methods are used as templates for subclass method overloading, and all methods in the inherited abstract class must be implemented.

Abstract classes and implementation examples of abstract classes are as follows:

The code is as follows:

<?php
abstract class User{  //定义抽象类
    abstract protected function getUser(); //定义抽象方法
    public function print_content(){
        print $this->getUser();
    }
}
class vipUser extends User{
    protected function getUser(){
        return "抽象类与抽象方法www.jb51.net";
    }
}
$user=new vipUser(); //实例化子类
$user->print_content(); //抽象类与抽象方法
?>

Note: When an abstract class inherits another abstract class (the purpose is to extension), you cannot override the abstract method of the parent class.

In PHP5.1, static abstract methods are supported in abstract classes. In the example below, we see that static abstract methods can be declared. When implementing this method, it must be a static method.

The code is as follows:

<?php
abstract class User{
 protected static  $sal=0;
 static abstract function getSal();
 static abstract function setSal($sal); 
}
class VipUser extends User{
 static function getSal(){
  return self::$sal;
 }
 static function setSal($sal){
  self::$sal=$sal;
 }
}
VipUser::setSal(100);
echo "you sal is www.jb51.net " . VipUser::getSal();
?>

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