A brief discussion on object-oriented inheritance in PHP

This article will introduce you to PHP object-oriented inheritance. It has certain reference value. Friends in need can refer to it. I hope it will be helpful to everyone.

1. Introduction

1. Inheritance is a mechanism to obtain one or more classes from a base class, which can realize Reuse of classes

2. Subclasses will inherit the attributes and methods of the parent class, and can extend the parent class

2. How to inherit a class

1. PHP is single inheritance. A class can only inherit one parent class, but a parent class can be inherited by multiple subclasses.

2. Subclasses cannot inherit the private properties and private methods of the parent class

## 3. Class methods can be inherited, and class constructors can also be inherited

4 . Inheritance method: use the extends keyword

//定义一个基类
class Book{
	public $name;
	public $price;
	private $page;
	public function __construct($name){
		$this->name = $name;
	}
	public function getName(){
		return $this->name;
	}
}

//定义一个子类，并继承基类
class NoteBook extends Book{

}

//实例化子类，并继承基类构造方法
$notebook = new NoteBook('book');

//子类继承的属性
echo $notebook->name;//结果为book

//子类继承的属性
echo $notebook->getName();//结果为book

//子类不能访问基类的私有属性
echo $notebook->page; //错误

3. How to inherit a class

1. You can add a modifier in front of the attributes and methods of the class. To control some access to the class

2. private: cannot be directly called externally, but can only be called inside the current class

3. protected: the modified properties and methods can only be called Called by the current class or subclasses, it cannot be called by the outside world

4. public: modified properties and methods can be called without restriction

4. Overriding

1. If the method inherited from the parent class cannot meet the needs of the subclass, it can be rewritten. This process is called method rewriting.

2. Methods overridden in subclasses cannot use more restrictive access rights than the overridden methods in the parent class.

3. The construction method of the parent class can also be rewritten.

//定义一个子类，并继承基类
class NoteBook extends Book{
//覆写基类的方法
public function getName(){
return 'The book name is'.$this->name;
}
}

5. parent:: keyword

1. Use parent:: to reference the method of the parent class, and it can also be used to call the method defined in the parent class. member methods.

public function getName(){
//调用父类的方法
return 'The book name is '.parent::getName();
}

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