Expt 1 - Part 1, Part 2 & Part 3

Explanation

This Java code demonstrates the very basic concepts of classes and objects. It defines a blueprint for a Box and then creates an actual Box to perform a simple calculation: finding its volume.

1. class Box { ... }: This section defines a class named Box. Think of a class as a blueprint or a template. It doesn't create an actual box yet, but it describes what a Box will look like and what properties it will have. In this case, every Box will have three properties: width, height, and depth, all of which are double (decimal) numbers. These properties are called instance variables because each instance (object) of the Box class will have its own set of these variables.

2. class BoxDemo1 { ... }: This is another class, BoxDemo1, which serves as the "driver" class for our program. It contains the main method, which is the starting point for every Java application.

3. public static void main(String args[]) { ... }: This is the main method. When you run the BoxDemo1 class, the code inside this method is executed first.

4. Box mybox = new Box();: This is a crucial line. Here, we are creating an object (an instance) of the Box class.

   • new Box(): This part actually creates a new Box in the computer's memory based on the Box blueprint.
   • Box mybox = ...: This declares a variable named mybox of type Box and assigns the newly created Box object to it. Now, mybox is a concrete instance that has its own width, height, and depth.

5. double vol;: A double variable named vol is declared to store the calculated volume.

6. mybox.width = 5;, mybox.height = 10;, mybox.depth = 15;: These lines are accessing the instance variables of the mybox object. The . (dot) operator is used to access members (variables or methods) of an object. We are assigning specific values (5, 10, and 15) to the width, height, and depth properties of this particular mybox object.

7. vol = mybox.width * mybox.height * mybox.depth;: Here, the volume is calculated by multiplying the width, height, and depth values that belong to the mybox object. The result is stored in the vol variable.

8. System.out.println("Volume is " + vol);: Finally, this line prints the calculated volume to the console. The string "Volume is " is concatenated with the value of vol and then displayed.

In essence, this code defines what a box is, then builds one specific box, gives it dimensions, and calculates its volume.

Algorithm

The algorithm used in this code can be described as follows:

1. Define a Class (Blueprint): Create a class named Box that serves as a blueprint for a three-dimensional box.
   • Declare three instance variables within Box: width, height, and depth, all of type double.
2. Define a Driver Class: Create a class named BoxDemo1 to contain the main execution logic.
3. Entry Point: Implement the main method within BoxDemo1, which is the starting point of the program.
4. Instantiate an Object: Inside the main method, create a new object (an instance) of the Box class. Let's call this object mybox.
5. Declare a Variable: Declare a double variable named vol to store the calculated volume.
6. Assign Values to Object Properties: Assign specific numerical values to the width, height, and depth instance variables of the mybox object.
   • Set mybox.width to 5.
   • Set mybox.height to 10.
   • Set mybox.depth to 15.
7. Calculate Volume: Compute the volume by multiplying the width, height, and depth of mybox. Store the result in the vol variable.
8. Display Result: Print the calculated volume to the console, preceded by a descriptive message.