菜鸟求救!(non-static variable this cannot be referenced from a static context)

Question

解决办法一：不要把Car做成内部类即可
办法二：CarDemo.Car Democar= new CarDemo().new Car();

Answer 1

Car被定义成CarDemo中的内部类，在静态方法main里头，无法调用CarDemo中定义的成员，尽管这个成员是一个类。你可以这样：
public class CarDemo 
{
public static void main(String[] args) 
{
//Car Democar= new Car();
//Democar.set_number(3838);
//Democar.show_number();
                  Cardemo d=new CardDemo();
                  d.useCar();
}

public void useCar(){
Car c=new Car();
                  c.set_number(03838);
                  c.shown_number();
} class Car
{
int car_number; void set_number(int car_num)
{
car_number=car_num;
} void show_number()
{
System.out.println("My car No. is:"+car_number);
}
}
}