How to use inheritance of php classes to solve code duplication

This article mainly introduces the use of classes in PHPInheritance to solve the problem of code duplication. The examples analyze the principles and usage techniques of inheritance. It is of great practical value. Friends in need can refer to it

The example in this article describes the use of class inheritance in PHP to solve the problem of code duplication. Share it with everyone for your reference. The specific analysis is as follows:

Inheritance simply means to create one or more subclasses for a class. To create a subclass, you must use the extends keyword in the class declaration. The new class name is in in the front, extends in the middle, and the parent class name in the back.

In the following example, we create two new classes, BookProduct and Cdproduct, both of which inherit from the ShopProduct class.

<?php
header(&#39;Content-type:text/html;charset=utf-8&#39;);
// 从这篇开始，类名首字母一律大写，规范写法
class ShopProduct{    // 声明类
 public $numPages;   // 声明属性
 public $playLenth;
 public $title; 
 public $producerMainName;
 public $producerFirstName;
 public $price;
 function construct($title,$firstName,$mainName,$price,$numPages=0,$playLenth=0){
  $this -> title = $title;    // 给属性 title 赋传进来的值
  $this -> producerFirstName= $firstName; 
  $this -> producerMainName = $mainName; 
  $this -> price= $price; 
  $this -> numPages= $numPages; 
  $this -> playLenth= $playLenth; 
 }
 function getProducer(){    // 声明方法
  return "{$this -> producerFirstName }"."{$this -> producerMainName}";
 }
 function getSummaryLine(){
  $base = "{$this->title}( {$this->producerMainName},";
  $base .= "{$this->producerFirstName} )";
  return $base;
 }
}
class CdProduct extends ShopProduct {
 function getPlayLength(){
  return $this -> playLength;
 }
 function getSummaryLine(){
  $base = "{$this->title}( {$this->producerMainName},";
  $base .= "{$this->producerFirstName} )";
  $base .= "：playing time - {$this->playLength} )";
  return $base;
 }
}
class BookProduct extends ShopProduct {
 function getNumberOfPages(){
  return $this -> numPages;
 }
 function getSummaryLine(){
  $base = "{$this->title}( {$this->producerMainName},";
  $base .= "{$this->producerFirstName} )";
  $base .= "：page cont - {$this->numPages} )";
  return $base;
 }
}
?>

Since the subclass does not define a constructor method, when the BookProduct and Cdproduct classes are instantiated, the constructor of the parent class ShopProduct will be automatically called.

The subclass inherits all the public and protected methods and properties of the parent class by default (but does not inherit the private methods and properties. The functions of these three keywords will be discussed later). That is, we can call the getProducer() method in an object instantiated from the Cdproduct class, even though getProducer() is defined in the ShopProduct class.

Add the following code to the above:

$product2 = new CdProduct("PHP面向对象","郭","碗瓢盆",7,null,"7小时");
print "美好生活：{$product2 -> getProducer()}<br>";
// 结果是：美好生活：郭碗瓢盆

Both subclasses inherit the public parts of the parent class, but note that both the BookProduct and Cdproduct classes override the getSummaryLine() method, providing It has its own unique implementation, indicating that subclasses can expand and modify the functions of parent classes.

But the implementation of this method in the parent class seems a bit redundant, because both of its subclasses have overridden this method, but other subclasses may use its basic functions. The existence of this method provides guarantees for client code: all ShopProduct objects will have a getSummaryLine() method, and both BookProduct and CDproduct use their respective getSummaryLine() methods to access the $title property.

Perhaps at the beginning, inheritance is a concept that is not easy to understand. First of all, we can know that by defining a class that inherits from other classes, we ensure that a class has its free functions and the functions of the parent class. Then there is the "search" function of the subclass. When we call $product2 -> getProducer(), the getProducer() method is not found in the CdProduct class, so we look for this method in the ShopProduct class and call it if it is. If not, an error will be reported. The same goes for accessing properties.

Looking at the construction method of ShopProduct, you will find that we are still managing the data that should be processed by the subclass in the base class (parent class): BookProduct should handle the $numPages parameters and properties; Cdproduct should handle $playLength Parameters and properties. To accomplish this, we need to define constructors separately in the subclass.

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