Please Help.explain this. why? how?

Question

class Program {
int x=2;
int z=f(f(x));

int f(int x){
return x+x;
}
public static void main(String[] args) {
Program obj = new Program() ;
System.out.println(obj.z);
}
}

Answer 1

f(2)=2+2=4
f(4)=4+4=8

Output is 8.

Answer 2

The output would be 8. When you creating a new object it sets x=2. And then it calls a function to evaluate z. But in first function call the parameter is the number, that a subfunction should return.
z=f(f(x))=f(x+x)=f(2+2)=f(4)=4+4=8.

Answer 3

Thanks all.