How to convert php parent class to subclass

In the process of object-oriented programming, class inheritance is a very important concept. Inheritance enables code reuse, saving programmers time and energy. However, there are often situations where you need to use an existing parent class, but also add or change some unique methods and attributes of the subclass. At this time, the need for "parent class rotor class" emerges urgently. This article will explore how to convert Php parent class to subclass.

Why Php parent class rotor class

In the process of programming, we often find that certain classes are very suitable for our needs, but these classes lack some methods and attributes we need . If we directly modify the original parent class, our modified class will become a brand new class. Therefore, we inevitably need to create a new subclass and inherit most of its properties and methods from the existing parent class. In this case, the requirement of "parent class to child class" will appear.

How to implement the Php parent class rotor class

The implementation of the Php parent class rotor class can use a keyword called extends. The extends keyword in Php is used to implement inheritance. Its usage is as follows:

class ChildClass extends ParentClass {
  //子类的属性和方法
}

Through the extends keyword, we can inherit most of the methods and properties of the parent class into our subclasses, and at the same time Add the new methods and properties we need to ChildClass.

Actually, this method implements an inheritance relationship, rather than the true conversion of "parent class to subclass". Therefore, we need to pay attention to the following points:

1. The subclass must contain the constructor of the parent class
   Inheritance implemented through extends, the subclass must contain the constructor of the parent class. In Php, subclasses automatically inherit the constructor of the parent class, so we do not need to explicitly declare the same constructor in the subclass.
2. The subclass must call the constructor of the parent class
   In order to ensure that the members in the parent class can be initialized normally, the subclass must call the corresponding parent class constructor in the constructor. This is a common problem in many libraries.

The following is a simple example that illustrates how to convert Php parent class to subclass:

class MyBaseClass {
  private $myBaseVar;
  
  public function __construct(){
    echo "Construction of Base class\n";
    $this->myBaseVar = "Initial value";
  }
  
  public function getMyBaseVar() {
    return $this->myBaseVar;
  }
}

class MySubClass extends MyBaseClass {
  private $mySubVar;
  
  public function __construct(){
    echo "Construction of Sub class\n";
    parent::__construct();
    $this->mySubVar = "Another value";
  }
  
  public function getMySubVar() {
    return $this->mySubVar;
  }
}

$obj = new MySubClass();
echo $obj->getMyBaseVar() . "\n";
echo $obj->getMySubVar() . "\n";

In this example, we first define a class called MyBaseClass Base class, which has a private member variable named myBaseVar. In order to obtain the value of the myBaseVar variable, we implement the getMyBaseVar() member function.

Then we define a class called MySubClass, which inherits from MyBaseClass. In order to meet the constructor requirements of MyBaseClass, we use parent::__construct() in the constructor to explicitly call the constructor in MyBaseClass. Similarly, we also added a private member variable named mySubVar and implemented the getMySubVar() member function.

Finally we created a MySubClass example named $obj and tested the effect of the two member functions getMyBaseVar() and getMySubVar(). The output is as follows:

Construction of Sub class
Construction of Base class
Initial value
Another value

As can be seen from the output, the constructor of the parent class was successfully called, and the subclass not only obtained the properties of the myBaseVar variable of the parent class, but also added a variable named mySubVar. Private property.

Conclusion

When we need to extend an existing class, we can create a subclass that inherits the parent class. Through inheritance, subclasses can obtain most of the properties and methods of the parent class, and we can also add new properties and methods to the subclass. By using parent::__construct() in the constructor, we can ensure that the constructor in the parent class is successfully called, thus ensuring that the members in the parent class can be initialized normally. The above is the implementation method of Php parent class rotor class. I hope it will be helpful to learners of Php programming.

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