What is interface?

Object interfaces allow you to create code which specifies which methods a class must implement, without having to define how these methods are handled.

Interfaces are defined using the interface keyword, 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. 

<?php
// Declare the interface 'iTemplate'interface iTemplate{
    public function setVariable($name, $var);
    public function getHtml($template);
}
// Implement the interface
// This will workclass Template implements iTemplate{
    private $vars = array();
 
    public function setVariable($name, $var)
    {
        $this->vars[$name] = $var;
    }
 
    public function getHtml($template)
    {
        foreach($this->vars as $name => $value) {
            $template = str_replace('{' . $name . '}', $value, $template);
        }

        return $template;
    }
}
// This will not work
// Fatal error: Class BadTemplate contains 1 abstract methods
// and must therefore be declared abstract (iTemplate::getHtml)class BadTemplate implements iTemplate{
    private $vars = array();
 
    public function setVariable($name, $var)
    {
        $this->vars[$name] = $var;
    }
}?>