inanzzz | S.O.L.I.D. Interface Segregation principle

An interface should never become a general purpose interface. A class specific interface is always better than one general purpose interface.

# VIOLATION
interface PlayerInterface
{
    public function run();
    public function jump();
    public function rebound();
}

class Basketball implements PlayerInterface
{
    public function run() {}
    public function jump() {}
    public function rebound() {}
}

class Football implements PlayerInterface
{
    public function run() {}
    public function jump() {}
    public function rebound() {}
}

As you can see above, Football class is forced to implement rebound method which has nothing to do with it. This is a violation.

# REFACTORED
interface PlayerInterface
{
    public function run();
    public function jump();
}

interface BasketballPlayerInterface
{
    public function rebound();
}

class Basketball implements PlayerInterface, BasketballPlayerInterface
{
    public function run() {}
    public function jump() {}
    public function rebound() {}
}

class Football implements PlayerInterface
{
    public function run() {}
    public function jump() {}
}

As you can see above, we have moved rebound method into BasketballPlayerInterface interface and let only Basketball class implement it. Our Football class is not forced to implement irrelevant methods anymore.