Expt 1 - Part 1, Part 2 & Part 3

Explanation

This Java code is designed to calculate and display the area and perimeter (circumference) of a circle. It first asks the user to input the radius of the circle, then uses this value along with a predefined approximation of pi (3.14) to perform the calculations.

Let's break down the logic step by step:

1. Import Scanner: The line import java.util.Scanner; brings in the Scanner class, which is a utility in Java used for reading input from various sources, including the user's keyboard (console).
2. Class Definition: class prog7 defines a class named prog7. In Java, all code resides within classes. This class will contain the main logic of our program.
3. Main Method: public static void main(String args[]) is the entry point of any Java application. When you run this program, execution begins inside this main method.
4. Create Scanner Object: Scanner input = new Scanner(System.in); creates an instance of the Scanner class. System.in represents the standard input stream, typically your keyboard. This input object is now ready to read data typed by the user.
5. Define Pi: double pi = 3.14; declares a variable named pi of type double (which can store decimal numbers) and initializes it with the value 3.14. This is an approximation of the mathematical constant Pi.
6. Prompt for Radius: System.out.print("Radius of Circle: "); displays the message "Radius of Circle: " on the console. System.out.print does not add a new line after the message, so the user's input will appear on the same line.
7. Read Radius Input: double r = input.nextInt(); reads an integer value typed by the user from the console. Although nextInt() reads an integer, the result is stored in a double variable r. Java automatically converts the integer to a double in this case. This r now holds the radius of the circle.
8. Calculate and Print Area: System.out.println("Area of Circle: "+(pi*r*r)); calculates the area of the circle using the formula π * r * r (or πr²). The result of this calculation is then combined (concatenated) with the string "Area of Circle: " and displayed on the console. System.out.println adds a new line after printing.
9. Calculate and Print Perimeter: System.out.println("Perimeter of Circle: "+(2*pi*r)); similarly calculates the perimeter (circumference) using the formula 2 * π * r. This result is also concatenated with a descriptive string and printed to the console on a new line.
10. Close Scanner: input.close(); is an important step that releases the system resources associated with the Scanner object. It's good practice to close resources like scanners when they are no longer needed to prevent resource leaks.

Algorithm

The algorithm used in this program can be described in the following steps:

1. Start the Java program.
2. Initialize a Scanner object to read input from the standard input stream (keyboard).
3. Declare a double variable named pi and assign it the approximate value 3.14.
4. Display a prompt message to the user asking for the radius of the circle.
5. Read the integer value entered by the user from the console and store it in a double variable named r.
6. Calculate the area of the circle using the formula Area = pi * r * r.
7. Display the calculated area, preceded by a descriptive label, on the console.
8. Calculate the perimeter (circumference) of the circle using the formula Perimeter = 2 * pi * r.
9. Display the calculated perimeter, preceded by a descriptive label, on the console.
10. Close the Scanner object to release system resources.
11. End the program.