Java interfaces

gistfile1.java

public interface Weapon {
    public boolean fire();
    
    public void reload();
}

public interface Vehicle {
    public void drive(int distance);
}

public class Tank implements Vehicle, Weapon {
    private int position = 0;
    private int ammo = 1;
    public boolean fire() {
        if (ammo > 0) {
            ammo -= 1;
            return true;
        } else {
            return false;
        }
    }
    
    public void reload() {
        ammo = 1;
    }
    
    public void drive(int distance) {
        position += distance;
    }
}

public class FireArm implements Weapon {
    private int ammo = 20;

    public boolean fire() {
    if (ammo > 0) {
        ammo -= 1;
        return true;
    } else {
        return false;
    }
    
    public void reload() {
        ammo = 20;
    }
}

public class Car implements Vehicle {
    private boolean direction = 0;
    private double x = 0, y = 0;
    
    public void drive(int distance) {
        double xT += Math.sin(direction) * d;
        double yT += Math.cos(direction) * d;
        x = xT;
        y = yT;
    }
}