Interface

InterfaceShubhangi ShindeInterfacesObject interfaces allow you to create code which specifies which methods a class must implement, without having to define how these methods are handled.Byimplementinginterface you are forcing any class to must declaring some specific set of methods in oopAn interface simply lists (function prototype) the methods a class must implement. However, in PHP a class can implement multiple interfaces and these interfaces can also be used in type hinting.Interfaces are defined using theinterfacekeyword, in the same way as a standard class, but without any of the methods having their contents defined.All methods declared in an interface must be public; this is the nature of an interface.To implement an interface, theimplementsoperator is used. All methods in the interface must be implemented within a class; failure to do so will result in a fatal error. Classes may implement more than one interface if desired by separating each interface with a comma.interface Countable{public function count();}class MyThings impmplements Countable{public function count();{return count($this->arrayofThings);}}Interface exampleDifferencesbetween abstract class and interface in PHP

In abstract classes this is not necessary that every method should be abstract. But in interface every method is abstract.Multiple andmultilevelboth type of inheritanceis possible in interface. But single and multilevelinheritanceis possible in abstract classes.Method of php interface must be public only. Method in abstract class in php could be public or protected both.In abstract class you can define as well as declare methods. But in interface you can only define your methods.

Final classes and methodsFinal classes :In some cases you may want to prevent a class from being inherited from or a function to be overridden. This can be done with the final keyword, which simply causes PHP to throw an error if anyone tries to extend your final class or override your final function.A final class is a class that cannot be extended. To declare a class as final, you need to prefix the class keyword with final.final class BaseClass { public function myMethod() { echo "BaseClass method called"; } } //this will cause Compile error class DerivedClass extends BaseClass { public function myMethod() { echo "DerivedClass method called"; } } $c = new DerivedClass(); $c->myMethod();Final Method

A final method is a method that cannot be overridden. To declare a method as final, you need to prefix the function name with the final keyword.A normal method (public or protected) can be overridden in the child class. If you want a method to remain fixed and unchanging, prefix the definition with thefinalkeyword.A final method cannot be overridden.class BaseClass { final public function myMethod() { echo "BaseClass method called"; } } class DerivedClass extends BaseClass { //this will cause Compile error public function myMethod() { echo "DerivedClass method called"; } } $c = new DerivedClass(); $c->myMethod();When to declare a class as final

You should declare a class as final when you think that you implementation of that class should not change in the derived class. You should do this mainly for Utility classes where you dont want the behavior /implementation of your class to change.When to declare a method as final

You should declare a class method as final when you think that the method you develop contains necessary functionality to support your application and any modification or change to the functionality can cause unexpected errors/bugs.