How to Write Robust Programs with the Help of Loops in Java?

Here, we are going to examine using loops to develop more efficient code. It is commonly accepted that implementing loops to solve a problem statement is an imprudent strategy. Despite this, there can be an abundance of scope for trial and error here. To put it simply, a loop statement allows us to run a statement or set of statements multiple times. Additionally, we are able to design strong codes and modify their execution to correspond with our needs. Ensuring that our code can gracefully handle a variety of edge circumstances, user mistakes, and unexpected inputs is essential to designing robust programs. Robustness can be considerably enhanced with the judicious use of loops.

Example 1:

Let us say that we want to determine a rectangle's area and perimeter. A rookie programmer would generally start by determining whether the length is larger than zero. Should that not be the case, print a non-zero positive integer. What flaws are there now? The program will print an enter non-zero positive integer and terminate its execution if the user repeatedly enters a number that is less than or equal to zero. In this case, we must repeatedly compile our code.

Implementation:

FileName: AreaOfRectangleExample1.java

import java.io.*;
import java.util.Scanner;
public class AreaOfRectangleExample1
{
    public static void main(String[] args) 
    {
        // Creating a Scanner class 
        // object to receive input
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter the length of the rectangle:");
        double length = sc.nextDouble(); 
        System.out.println("Enter the width of the rectangle:");
        double width = sc.nextDouble(); 
        double perimeter_rect; 
        double area_rect;
        // Verify that the width and length
        // are both positive.
        if (length <= 0 || width <= 0) 
        {
            System.out.println("Please provide positive numbers that are not zero."); 
        } 
        else 
        { 
            // Determining the perimeter and 
            // area of the rectangle
            perimeter_rect = 2 * (length + width);
            area_rect = length * width;
            // Print and display the perimeter 
            // and area of  the rectangle
            System.out.println("Perimeter of the rectangle: " + perimeter_rect);
            System.out.println("Area of the rectangle: " + area_rect); 
        }
    }
}

Output:

Enter the length of the rectangle:
-5
Enter the width of the rectangle:
-6
Please provide positive numbers that are not zero.

Explanation:

We observed in the example above that we would have to constantly compile and run the program whenever the user entered any non-zero or negative integers. The while loop can be used to avoid this difficult circumstance. We can write substantial code and control its execution to meet our needs by using loops.

Example 2:

The given Java program uses the user-inputted length and width as parameters to calculate and display the area and perimeter of a rectangle. When both dimensions are positive, the area is calculated as length * width and the perimeter as 2 * (length + width). The results are then shown. The user is prompted to enter the numbers again until they give the correct positive dimensions if the entered dimensions are not positive. Prior to carrying out the mathematical calculations, the loop makes sure that the inputs are continuously verified.

Implementation:

FileName: AreaandPerimeterRectangleExample2.java

import java.util.Scanner;
import java.io.*;
public class AreaandPerimeterRectangleExample2 
{
    public static void main(String[] args) 
    {
        // Custom input - A rectangle's width and length
        double length = 10;
        double width = 5;
        Scanner scanner = new Scanner(System.in);
        System.out.println("Enter the Length of the rectangle:");
        length = Double.parseDouble(scanner.nextLine());
        System.out.println("Enter the Width of the rectangle:");
        width = Double.parseDouble(scanner.nextLine());
        // As length and width are greater than Integer.MIN_VALUE,
        // This while loop will continue to run.
        while (length > Integer.MIN_VALUE && width > Integer.MIN_VALUE) 
        {
            // Verify that the width and length are both positive.
            if (length > 0 && width > 0) 
            {
                double perimeter_rect = 2 * (length + width);
                double area_rect = length * width;
                System.out.println("Perimeter of the rectangle: " + perimeter_rect);
                System.out.println("Area of the rectangle: " + area_rect);
                break;
            }
            // Notify the user if the width or length is not positive.
            System.out.println("Please specify length and width in non-zero positive numbers.");
            System.out.println("Enter Length of the rectangle:");
            length = Double.parseDouble(scanner.nextLine());
            System.out.println("Enter Width of the rectangle:");
            width = Double.parseDouble(scanner.nextLine());
        }
    }
}

Output:

Enter the Length of the rectangle:
-5
Enter the Width of the rectangle:
10
Please specify length and width in non-zero positive numbers.
Enter Length of the rectangle:
6
Enter Width of the rectangle:
5
Perimeter of the rectangle: 22.0
Area of the rectangle: 30.0