Write a program to show use and advantages of Constructor in Java

Write a program to show use and advantages of Constructor in Java

class Box {

                        double l;

                        double b;

                        double h;

                        Box() {

                                    l=2.3;

                                    b=3.4;

                                    h=4.5;

                        }

                        void show() {

                                    System.out.print("the volume of the box is : " +(l*b*h));

                        }

}

class volume {

                        public static void main(String args[]) {

                                    Box o=new Box();

                                    o.show();

                        }

             }