Abstract classes and interface definitions in PHP

Abstract class:

　1) A class containing at least one abstract method (abstract function). In other words, any class that has only one or more abstract methods is an abstract class.

　2) In an abstract class, can have concrete methods, and can have member variables.

　3) Abstract classes cannot be instantiated . They are all called abstract, so how can they be instantiated? 2333.

　4) Usage:

　　abstract class Father{

protected (or public modification cannot be private, otherwise subclasses will not be able to obtain it) abstract function func1();

　　}

　When implementing the inherited abstract method

　　class Son extends Father{//

Like ordinary classes, a subclass can only inherit one abstract class

　　public (remove abstract keyword) function func1{

　　　　echo '

must implement all abstract methods';

　　　}

　　}

Interface:

　1) The interfaces

are all abstract methods . (Because it is used to implement subclasses. So it must be public.)

　2) The interface

cannot have specific methods , and can only have member constants .

　3) A class

can implement multiple interfaces .

　3) Usage:

Implement multiple interfaces after the implements keyword separated by commas.

　　class Son

implements InterfaceA,InterfaceB,InterfaceC {

　　　 // 1. Implement

all abstract methods of these three interfaces, 2. Be completely consistent with the parameters of the abstract methods 3. The constants of the interface cannot be overwritten .

　　}