将接口注入php类

Question

So I have the following interface defined for a car:

interface FuelTank
{
    public function useFuel();
}

interface WaterTank
{
    public function useWater();
}

interface CarInterface extends FuelTank, WaterTank
{
    public function drive($miles);

    public function setFuelTank(FuelTank $tank);

    public function setWaterTank(WaterTank $tank);
}

I have tried to build a class that implements and complies to the CarInterface but I'm having trouble with the injection of the FuelTank and Watertank dependancies. This is the class I came up with:

class Car implements CarInterface
{
    protected $fuelTank;
    protected $waterTank;

    public function drive($miles)
    {
        return $miles;
    }

    public function useWater()
    {

    }

    public function useFuel()
    {

    }

    public function setFuelTank(FuelTank $tank)
    {
        $this->fuelTank = $tank;
    }

    public function setWaterTank(WaterTank $tank)
    {
        $this->waterTank = $tank;
    }
}

Now when I run the following:

$car = new Car;
$car->setFuelTank(new FuelTank);

I get this message:

Fatal error: Cannot instantiate interface FuelTank

I also can't declare the class FuelTank as I get this error instead:

Fatal error: Cannot redeclare class FuelTank

Can someone help me understand how to correctly implement the interface above and what's going on here?

Answer 1

You should rename the interface FuelTank to FuelTankInterface and declare a class FuelTank which implements the FuelTankInterface. An interface cannot be instantiated.