The PHP implements keyword is used to declare that a class must have the methods described in the specified interface (called polymorphism).

<?php
interface Machine {
    public function activate();
    public function deactivate();
    public function isActive();
}

class Kettle implements Machine {
    private $isOn = false;

    public function activate() {
        $this->isOn = true;
    }

    public function deactivate() {
        $this->isOn = false;
    }

    public function isActive() {
        return $this->isOn;
    }
}

$machine = new Kettle();

$machine->activate();

if($machine->isActive()) {
    echo 'The machine is on';
}
else {
    echo 'The machine is off';
}

echo '<br>';

$machine->deactivate();

if($machine->isActive()) {
    echo 'The machine is on';
}
else {
    echo 'The machine is off';
}
?>