can someone explain to me what does the dot mean ? and what would be the output and explain it?

import java.io.*; public class Green { private int a; private int b; public Green(int aa,int bb) { a=aa; b=bb; } public void equals(Green c) { this.a=c.a;this.b=c.b;} public void fn(Green c) { this.a=3*c.b-c.a; this.b=2*c.a-this.b;} public void gg() { this.b=this.b-1; this.a=this.b-2; } public static void main(String args[]) { Green x=new Green(2,2); Green y=new Green(2,1); Green z=new Green(1,4); int xx=1,yy=2,zz=3; x.fn(y); z.gg(); System.out.println(" Value of x.a is = " +x.a); System.out.println(" Value of x.b is = " +x.b); System.out.println(" Value of z.b is = " +z.b); } }