Example PHP Interface class

gistfile1.php

<?php

//Define a new Interface for all 'shapes' to inherit
interface Shape {

  //Define the methods required for classes to implement
  public function getColor();

  public function setColor($color);    

  //Interfaces can't define common functions so we'll just
  //define a method for all implementations to define
  public function describe();

}

//Define a new 'Triangle' class that inherits from the
//'Shape' interface
class Triangle implements Shape {

  private $color = null;

  //Define the required methods defined in the abstract
  //class 'Shape'
  public function getColor() {
      return $this->color;
  }   

  //Note that the method signature matches the abstract
  // class with only one parameter
  public function setColor($color) {
      $this->color = $color;
  }   

  //Interface can't have common functions so they must be defined
  //within the child class
  public function describe() {
      return sprintf("I'm an %s %s\n", $this->getColor(), get_class($this));
  }   
}

//Instantiate the Triange class
$triangle = new Triangle();

//Set the color
$triangle->setColor('Orange');

//Print out the value of the describe common method
//provided by the abstract class
//Will print out out "I'm an Orange Triange"
print $triangle->describe();