Understand the object-oriented inheritance mechanism of PHP

Understand PHP object-oriented inheritance mechanism

Inheritance is an important concept in object-oriented programming, which allows the creation of new classes that include the characteristics of old classes and function.

In PHP, inheritance can be achieved through the keyword extends. Through inheritance, subclasses can inherit the properties and methods of the parent class, and can add new properties and methods, or override inherited methods.

Let us understand the object-oriented inheritance mechanism of PHP through an example.

class Animal {
   public $name;
  
   public function eat() {
      echo "正在吃...";
   }
}

class Dog extends Animal {
   public function bark() {
      echo "正在汪汪叫...";
   }
}

$dog = new Dog();
$dog->name = "小黄";
$dog->eat();
$dog->bark();

In the above example, we first define an Animal class, which has a name attribute and an eat() method . Then, we created a Dog class and inherited the Animal class using the extends keyword. The Dog class adds a bark() method.

We created an instance of the Dog class $dog, and can assign a value to the name attribute of $dog . Because the Dog class inherits the Animal class, the $dog object can call the eat() method and bark()method.

One of the benefits of inheritance is that you can reuse code. Through inheritance, we can share the same properties and methods between multiple classes without writing the same code repeatedly. This makes the code more modular and easier to maintain.

Another benefit is that polymorphism can be achieved through inheritance. Polymorphism allows different behaviors to be implemented in different classes using the same method name. Let's illustrate this with an example.

class Animal {
   public function makeSound() {
      echo "动物发出声音...";
   }
}

class Dog extends Animal {
   public function makeSound() {
      echo "狗发出声音：汪汪汪...";
   }
}

class Cat extends Animal {
   public function makeSound() {
      echo "猫发出声音：喵喵喵...";
   }
}

$animal = new Animal();
$dog = new Dog();
$cat = new Cat();

$animal->makeSound();  // 输出：动物发出声音...
$dog->makeSound();  // 输出：狗发出声音：汪汪汪...
$cat->makeSound();  // 输出：猫发出声音：喵喵喵...

In the above example, we defined a Animal class and two subclasses Dog and Cat. They override the makeSound() method respectively. When we call the makeSound() method, which class method is called depends on the type of object.

This is a typical example of inheritance and polymorphism. Although they have the same method name, the code executed is different because of the overriding by the subclass. This allows us to dynamically decide which class method should be executed based on the actual situation.

Inheritance can also be extended through the constructor and destructor of the parent class. Subclasses can add additional logic before or after calling the parent class's constructor. Likewise, a subclass can do some processing before or after calling the parent class's destructor.

class Animal {
   public function __construct() {
      echo "Animal类的构造函数被调用...";
   }
  
   public function __destruct() {
      echo "Animal类的析构函数被调用...";
   }
}

class Dog extends Animal {
   public function __construct() {
      parent::__construct();
      echo "Dog类的构造函数被调用...";
   }
  
   public function __destruct() {
      echo "Dog类的析构函数被调用...";
      parent::__destruct();
   }
}

$dog = new Dog();

In the above example, we defined a Animal class and a Dog class. The Animal class has its own constructor and destructor, while the Dog class adds additional logic after calling the parent class's constructor and calling the parent class's destructor Some processing was added before.

When we create an instance of the Dog class, we will first call the constructor of the Animal class, and then call the Dog class's own constructor . When the object is destroyed, the destructors are called in the opposite order.

Inheritance is a very useful technique in object-oriented programming. It allows us to create more structured and modular code, improving code reusability and maintainability.

Through code examples, we have a deeper understanding of PHP's object-oriented inheritance mechanism. Hope this article helps you!

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