java extended class inheritance

Sum s = new Sum();
Sum.SetToZero z = new Sum.SetToZero();

Scanner input = new Scanner(System.in);
String read = input.nextLine();

while (!read.equals("end")) {

    if (read.equals("add")) {
        s.add()
    } 
    else if (read.equals("get")) {
        System.out.println(s.returnTotal());
    }
    else if (read.equals("zero")) {
        z.zero();
    }

   read = input.nextLine();
}

class:

public class Sum {

    int total = 0;

    public void add() {
        total += 1;
    }

    public int returnTotal() {
        return total;
    }

    public static class SetToZero extends Sum {

        public void  zero() {
            total = 0;
        }
    }
}

input:

add
add
zero
add
get
add
get
end

output:

3
4

output wanted:

1
2

Shouldn't the subclass inherit the total and set it to zero? What am I doing wrong? I know I could just move the zero into the main class but I want it to be in a separate class. thx for your help.

By making your total variable static, you can get the desired output.

class Sum {
    static int total = 0;
    public void add() {
        total += 1;
    }

    public int returnTotal() {
        return total;
    }

    public static class SetToZero extends Sum {
        public void  zero() {
            total = 0;
        }
    }
}

Apart from things pointed out in names like not using lowecase letters to start your class name; I think the reason why it's not working is because you're using two different variable instances for Sum and Sum.SetToZero. You don't need to create a new variables since SetToZero has all the attributes of Sum. I think you should change this:

Sum s = new Sum();
Sum.SetToZero z = new Sum.SetToZero();

Sum.SetToZero s = new Sum.SetToZero(); // use s for all operations 

Here is how your modified main method would look:

public static void main(String[] args) {
    Sum.SetToZero s = new Sum.SetToZero();

    Scanner input = new Scanner(System.in);
    String read = input.nextLine();

    while (!read.equals("end")) {

        if (read.equals("add")) {
            s.add();
        } 
        else if (read.equals("get")) {
            System.out.println(s.get());
        }
        else if (read.equals("zero")) {
            s.zero();
        }

        read = input.nextLine();
    }
}

When I ran this, I saw expected output:

src : $ java Sum
add
add
zero
add
get
1
add
get
2
end