<Variable>无法解析为变量

Question

I have the following code:

public interface CarInterface {

    int getCapacity();
    String getCarRegistration();
    void setCarRegistration(String registration);
    int getFuelAmmount();
    boolean isFull();
    boolean isRented();
    int addLitres(int litres);
    int drive();
}

---

public abstract class Car implements CarInterface{

    protected boolean full;
    private boolean rented;
    private String registration;
    protected int fuel;


    public String getCarRegistration() {
        return registration;
    }

    public void setCarRegistration(String registration){
        this.registration = registration;
    }


    public int getFuelAmmount() {
        return fuel;
    }

    public boolean isFull() {
        return full;
    }

    public boolean isRented() {
        return rented;
    }
}

---

public class LargeCar extends Car{

    public int drive() {
        return getFuelAmmount();
    }

    public int addLitres(int litres) {
        fuel = fuel + litres;
        if (fuel > 65) {
            fuel = 65;
        }
        if (isRented()) {
            int x = 5;
        }

        return x;


    }

    public int getCapacity() {
        return 65;
    }
}

Eclipse tells me that the return type is incompatible with the interface declaration (The return type is incompatible with CarInterface.addLitres(int)). I have no idea why this is. I said I'd return an int in the interface, and that's what I'm doing...

It also has a problem with 'x', which it says cannot be resolved to a variable. Oddly enough, when I take "int x" out of the if statement, the error message disappears.

Answer 1

You have to declare x outside the if .

int x = 0;
if (isRented()) {
   x = 5;
}

Answer 2

This here:

public int addLitres(int litres) {
        fuel = fuel + litres;
        if (fuel > 65) {
            fuel = 65;
        }
        if (isRented()) {
            int x = 5;
        }
        return x;
    }

is invalid since the variable x is in a limited scope just because is declared inside a if segment...

do instead: declare the int x as a variable in the method and set its corresponding value if fuel or whatever you need to chec

example:

 public int addLitres(int litres) {
        int x = 0;
        fuel = fuel + litres;
        if (fuel > 65) {
            fuel = 65;
        }
        if (isRented()) {
            x = 5;
        }
        return x;
    }

Answer 3

Well, you can't return x because it's not in scope to be returned since it is declared inside of the if(isRented()){int x = 5} code block. To return x you have to define it outside of the if(isRented()){int x = 5} scope like so

int x = 0;

if(isRented())
{
    x = 5;
}