Comparative introduction to class inheritance and interface inheritance in php

This article brings you a comparative introduction to class inheritance and interface inheritance in PHP. It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.

PHP class inheritance:

1. PHP classes do not support multiple inheritance, that is, subclasses can only inherit one parent class, but support multi-level inheritance, such as:

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 Inherited, but cannot be called by an instantiated object. If called, an error message "Call to protected method frist::printer()" will appear, and the parent class will put this method in protected mode

(3 ) The public method of the parent class can be inherited and called by the instantiated object, and it is a public method

(4) The subclass can override the public or protected method of the parent class, but cannot re-private the method. If the same name is used, just re-declare it 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 all public, and the default is public

(3) The class that references the interface must implement all the 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 implement.

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 class inherits and abstract class cannot override the parent class. 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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