The interface declares what methods a class must have without having to implement them. Any class that implements the interface will have to implement details of those declared methods. Interface is not a class, so you can not instantiate an interface. It is useful when you need to enforce some classes to do something.

• An interface is a description of the actions that an object can do.
• Interface is written in the same way as the class the declaration with interface keyword.

Rules of Interfaces:

• All methods declared in an interface must be public; this is the nature of an interface.
• All methods in the interface must be implemented within a class; failure to do so will result in a fatal error.
• The class implementing the interface must use the exact same method signatures as are defined in the interface
• Interfaces can be extended like classes using the extends operator.

Example for the interface class

<?php
	interface A {
		public function setProperty($x);
		public function description();
	}
	class Property implements A {
		public function setProperty($x) {
			$this->x = $x;
		}
		public function description() {
			echo "Counting" . $this->x . plot;
		}
	}
	$property = new Property();
	$property->setProperty(Garden);
	$property->description();
?>

Output:

Counting Garden plot

Interface can be extended with another interface using extends keyword

<?php
	interface A {
		public function Compute();
	}
	interface B extends A {
		public function Divide();
	}
	class C implements B {
		public function Divide() {
			$var=10;
			$var1=2;
			$var3=$var/$var1;
			echo “division of 10/2 is” . $var3;
		}
		public function Compute() {
			$a=2;
			$b=3;
			$c=$a*$b;
			echo “multiplication of 2*3 is” . $c;
		}
	}
	$obj = new C();
	$obj->Divide();
	$obj->Compute();
?>

Output:

division of 10/2 is 5
multiplication of 2*3 is 6

Interfaces Important Point:-

• We cannot create objects to interface, but the class implementing the interface can have objects
• We cannot define a variable in an interface.
• If we extend interface all the methods of the interface must be implemented in the child class.