What is the difference between class inheritance and interface inheritance in php

In PHP, the difference between class inheritance and interface inheritance is: PHP classes do not support multiple inheritance, that is, subclasses can only inherit one parent class, but support multi-level inheritance, while interfaces support multiple inheritance, that is, That is, an interface can inherit one or more interfaces.

The operating environment of this article: Windows 10 system, PHP version 7.1, Dell G3 computer.

What is the difference between class inheritance and interface inheritance in php

PHP class inheritance:

1. PHP classes do not support multiple inheritance, that is, subclasses can only inherit one. Parent class, but supports multi-level inheritance

For example:

class frist{
  public function __construct(){
    echo "我是第一个类。","<br>";
  }
  public function printer(){
    echo "frist","<br>";
  }
}
class seconds extends frist{}
class third extends seconds{}
$obj = new third();
$obj->printer();

Result: This is the first class. The second and third classes of frist do not override the printer() method. The printer() method can be called after the third class is instantiated.

2. Inheritance permission issues

(1) The private method of the parent class cannot be inherited, and the parent class is privatized

(2) The protected method of the parent class can be inherited, but It cannot be called by an instantiated object. If called, an error message "Call to protected method frist::printer()" will appear. The parent class puts this method in protected mode.

(3) The public method of the parent class can Inherited, can be called by instantiated objects, and is a public method

(4) Subclasses can override the public or protected methods of the parent class, but cannot re-private methods. If they have the same name, they can only be redeclared in this class

3. Interface class inheritance

(1) The interface supports multiple inheritance, and the methods of the interface class do not need to be implemented. For example:

interface frist{
  public function ex1();
}
interface seconds{
  public function ex2();
}
interface third extends frist,seconds{
  public function ex3();
}
class fourth implements third{
  public function ex1(){}
  public function ex2(){}
  public function ex3(){}
}
class fourth implements frist,seconds{
  public function ex1(){}
  public function ex2(){}
}

(2) The method permissions of the interface class are public, default public

(3) The class that refers to the interface must implement all methods of the interface, otherwise an error will be reported, such as: "Class e contains 1 abstract method and must therefore be declared abstract or implement the remaining methods", That is: class e contains 1 abstract method, so the remaining methods must be declared abstract or implemented.

4. Abstract class: As long as there is an abstract method in a class, then this class must be defined as an abstract class

(1) Abstract classes inherit and abstract classes cannot override parent classes. method.

(2) Abstract class inheritance is an expansion of the methods of the parent class.

(3) All abstract methods must be overloaded in the inherited derived class before they can be instantiated.

(4) Ordinary distribution implemented by abstract classes can be called directly in non-abstract subclasses.

5. Similarities and differences between interfaces and abstract classes (referring to the difference between abstract classes and interfaces)

(1) The use of interfaces is achieved through the keyword implements, and for abstract classes The operation is implemented using the keyword exotends of class inheritance

(2) The interface has no data members, but the abstract class has data members, and the abstract class can implement data encapsulation.

(3) The interface does not have a constructor, but the abstract class can have a constructor.

(4) The methods in the interface are all public types, while the methods in the abstract class can be modified with private, protected or public.

(5) A class can implement multiple interfaces at the same time, but can only implement one abstract class.

(6) Similarity: Nothing can be written in the function body, such as: function getName();.

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