Having error pls help on java

Question

Error; a reference to an enclosing class is required.
I want to print out the substraction class but when I create a new object of the class it gives me that error while an object of the Addition class works well
class Addition
{
int add(){
int a= 2;
int c= 3;
System.out.println(a + c);
return a + c;
}
class Substraction extends Addition
{
@Override
int add(){
int a= 2;
int b= 3;
System.out.println(a-b);
return a - b;
}
}
public static void main(String args[])
{
Substraction n= new Substraction();
n.add();
}
}

Answer 1

main() is static and can call only static methods and class variables, but you can create non-static object and call add() from this new object:
public static void main(String args[])
{
new Addition().main2();} void main2(){
Substraction n= new Substraction();
...
}

Answer 2

Cause you use non static variable in static method

Answer 3

Thanks