Interfaces

Inside Interfaces only methods can be defined.

The methods don't have body and must be declared in the classes that implement the interface.

Syntax

Defining interfaces:

interface InterfaceName { // code }

Implementing interface:

class ClassName implements InterfaceName

Example

<?php interface Vehicle { // Function that must be defined in // each class that extends the interface function getInsuranceCost($months); } class Car implements Vehicle { // Implementation of interface. public function getInsuranceCost($months) { return 25 * $months; } } class Bicycle implements Vehicle { // Implementation of interface. public function getInsuranceCost($months) { return 0; } } $car = new Car(); echo "Car's Year Insurance: " . $car->getInsuranceCost(12) . " $\n"; $bicycle = new Bicycle(); echo "Bike's Year Insurance: " . $bicycle->getInsuranceCost(12) . " $\n";

Output:

Car's Year Insurance: 300 $ Bike's Year Insurance: 0 $

Explanation:

• An interface is defined at lines 2 - 7.
• At line 6 a method is declared. This method must be declared in each class that implements the interface.
• At line 9 and 18 the classes Car and Bicycle implement the interface. For this reason they must define the function getInsuranceCost. If this is not done then the code won't execute.