Interface in PHP

Brief About Interface

Most of the design patterns use interfaces, but interfaces are no design pattern. So from the programming point of view it will not add any additional functionality to your code but it will help up to make some standards for the code you have written.

Interface is some what like as abstract class, you can find more about the abstract class from this article on Abstract in PHP.

Interface is just like a coding standard because interface allow us to create a code/class which specifies the list of methods a class must implement.

What can be declared in Interface?

We can declare methods and constants in interface. Make sure that declared method must have only declaration part and not the implementation part. Also all methods declared in interface must be public.

Note: All methods declared in interface must be public!!

How to Create Interface?

We can create an interface using the keyword [code]interface[/code]. Check out below code that will demonstrate the code to create an basic interface.

[cc lang=”php”]
interface first_interface
{
public function first_method($name);
public function second_method();
}
[/cc]

You can see that above interface have 2 methods declared. So any class which implement this interface must declare those two methods.

Implementing the Interface

Interface can be implemented using [code]implements[/code] operator. All methods declared in the interface must be implemented in class which implement that interface.

It will generate Fatal Error if you do not implement the method which declared in an interface. Please check below code which shows the implementation of the interface.

[cc lang=”php”]
interface first_interface
{
public function first_method($name);
public function second_method();
}

class new_class implements first_interface
{
public function first_method($name)
{
// Code goes Here for method
}

public function second_method()
{
// Code goes Here for method
}
}

[/cc]

We can implement more than one interface to one class. In this case interface names should be separated by comma [code],[/code].

[cc lang=”php”]
class new_class implements first_interface, second_interface
{
// Code for the class goes here.
}
[/cc]

Extending the Interface

Same as classes we can extend the interface too using the [code]extends[/code] keyword. So once any class implements the interface must implemets all methods from the both parent and child interfaces. Have a look at below code block for the same:

[cc lang=”php”]
interface first_interface
{
public function first_method($name);
}

interface second_interface extends first_interface
{
public function second_method();
}

// This class is implementing the second interface.
// And second_interface is exteding the first_interface.
// So this class needs to implement
// all methods declared in both interfaces.
class new_class implements second_interface
{
public function first_method($name)
{
// Code goes Here method
}

public function second_method()
{
// Code goes Here for method
}
}
[/cc]

Note: We can not implements two interfaces if same method declared in both interfaces.