Understanding the meaning of interfaces in php Interfaces

Everyone may understand this. I guess the meaning of this interface, which is used to call the interface content in the implementation class in the method called later, let's take a look at it later.
Pay. php Copy codeThe Code is as follows: interface Ipay
{
Function withmoney ();

// Function withinternet ();
}
Class Dmeng implements Ipay
{

Function withmoney ()
{
Echo "shopping in RMB ";
}
Function withinternet ()
{
Return "pay with online banking ";
}
}

Usei. phpCopy codeThe Code is as follows: include_once 'pay. php ';
Class main
{
Function run ($ vc)
{
$ This-> vc = $ vc;
$ This-> vc-> withinternet ();
Echo "yunxing ";
}

}
$ Com = new main ();
$ Com-> run (new Dmeng );

In the above way, We comment out a method in the interface and find that it is useless when we call it again.