class and object in java

/* A PROGRAM THAT USES Box CLASS.
CALL THIS PROGRAM AS BoxDemo.java */


class Box {
double width;
double height;
double depth;
}

// THIS CLASS DECLARES AN OBJECT OF TYPE Box.

class BoxDemo {

public static void main (String args[]) {

Box mybox = new Box();
double volume;

// assign values to the mybox's instance variables

mybox.width = 10;
mybox.height = 20;
mybox.depth = 15;

// compute volume of box

volume= mybox.width * mybox.height * mybox.depth;

System.out.println("Volume of the Box is:" +volume);
 }
}