Expt 1 - Part 1, Part 2 & Part 3

Explanation

This Java code demonstrates the fundamental concepts of classes and objects. It's designed to illustrate how to define a blueprint (a class) and then create multiple independent instances (objects) from that blueprint, each holding its own unique data.

Here's a step-by-step breakdown of what the code does:

1. Defining the Box Class:

   • The code first defines a class named Box. Think of Box as a blueprint or a template for creating boxes.
   • Inside this Box class, three variables are declared: double width;, double height;, and double depth;. These are called instance variables because each "box" object created from this blueprint will have its own separate width, height, and depth values. They define the state or characteristics of a Box object.

2. Defining the BoxDemo2 Class and main Method:

   • The BoxDemo2 class contains the public static void main(String args[]) method. This is the entry point of any Java application; execution begins here.

3. Creating Objects:

   • Inside main, the lines Box mybox1 = new Box(); and Box mybox2 = new Box(); are crucial. Here, two distinct objects named mybox1 and mybox2 are created from the Box class blueprint.
   • The new keyword is used to allocate memory for a new Box object, and Box() is a call to its constructor (a special method that initializes the object).
   • At this point, mybox1 and mybox2 are two separate, independent Box objects in memory, each with its own width, height, and depth variables, initially set to default values (0.0 for double).

4. Assigning Data to mybox1:

   • The lines mybox1.width = 5;, mybox1.height = 10;, and mybox1.depth = 15; assign specific dimension values to the width, height, and depth variables of the mybox1 object. The dot operator (.) is used to access the instance variables of a particular object.

5. Assigning Data to mybox2:

   • Similarly, mybox2.width = 20;, mybox2.height = 25;, and mybox2.depth = 30; assign different dimension values to the width, height, and depth variables of the mybox2 object. It's important to note that mybox1's dimensions remain unchanged; mybox2 has its own, separate set of data.

6. Calculating and Printing Volume for mybox1:

   • vol = mybox1.width * mybox1.height * mybox1.depth; calculates the volume using the dimensions stored in mybox1 and assigns the result to the vol variable.
   • System.out.println("Volume is " + vol); then prints this calculated volume to the console.

7. Calculating and Printing Volume for mybox2:

   • vol = mybox2.width * mybox2.height * mybox2.depth; calculates the volume using the dimensions stored in mybox2. This overwrites the previous value of vol.
   • System.out.println("Volume is " + vol); prints the volume of mybox2 to the console.

In essence, this code demonstrates how you can define a general structure (the Box class) and then create many specific items (the mybox1 and mybox2 objects) that conform to that structure, each with its own unique characteristics.

Algorithm

The program follows these steps:

1. Define a Class: Create a class named Box to serve as a blueprint for box objects.
2. Declare Instance Variables: Inside the Box class, declare three double type instance variables: width, height, and depth, to store the dimensions of each box.
3. Create Main Class: Define a class named BoxDemo2 which will contain the main method, the program's starting point.
4. Instantiate Objects: Inside the main method, create two separate objects (instances) of the Box class, named mybox1 and mybox2.
5. Declare Volume Variable: Declare a double variable named vol to store calculated volumes.
6. Assign Data to mybox1: Set specific values for the width, height, and depth instance variables of the mybox1 object.
7. Calculate and Print mybox1 Volume:
   • Calculate the volume of mybox1 by multiplying its width, height, and depth.
   • Store the result in the vol variable.
   • Print the message "Volume is " followed by the calculated volume of mybox1.
8. Assign Data to mybox2: Set different specific values for the width, height, and depth instance variables of the mybox2 object.
9. Calculate and Print mybox2 Volume:
   • Calculate the volume of mybox2 by multiplying its width, height, and depth.
   • Store the result in the vol variable (overwriting the previous value).
   • Print the message "Volume is " followed by the calculated volume of mybox2.