Java Program Demo 1: Factorials and Fibonacci Sequences

Hello everybody,

It’s Michael, and today’s Java post will be a little different from the previous six because I am not giving you guys a lesson today. See, when I launched this blog in June 2018, I said I was going to posts lessons and analyses with various programs. However, in the case of Java, I feel it is better to give you guys program demos that cover the concepts I’ve discussed so far (loops, if-else statements, etc.). In this post, I will show you guys two programs that cover all the Java concepts I’ve discussed so far.

Here is this code for the first program (video in link)-Fibonacci sequence program:

package javalessons;
import java.util.Scanner;

public class JavaLessons
{

public static void main(String[] args)
{
Scanner sc = new Scanner (System.in);
System.out.println(“Please choose a number: “);
int num = sc.nextInt();

int start = 0;
int t2 = 1;

if (num >= 0)
{
while (start <= num)
{
System.out.print(start + ” + “);

int sum = start + t2;
start = t2;
t2 = sum;
}
}

else
{
System.out.println(“Need a 0 or a positive number”);
}
}
}

This program prints every number in the Fibonacci sequence up to a certain point. If you’re wondering, the Fibonacci sequence is a pattern of numbers that starts with 0 and 1 and calculates each subsequent element by finding the sum of the two previous numbers.

• Here are the first 10 numbers of the Fibonacci sequence-0,1,1,2,3,5,8,13,21,34,55. Notice how every element after the 3rd is the sum of the previous two numbers (e.g. 13 is found by calculating 5+8-the two numbers that directly precede 13 in the series)

To calculate the Fibonacci sequence, I first ask the user to type in a number. That number will serve as the endpoint for my while loop where I calculate each element in the Fibonacci sequence; in other words, my while loop will find every element in the sequence until it reaches the closest possible number to the user’s input. For instance, if I wanted to find every number in the Fibonacci sequence stopping at 600, the program would stop at the closest possible number to 600-which is 377.

• I decided to add an endpoint because the Fibonacci sequence is infinite, and had I decided not to have an endpoint, I would’ve created an infinite loop.

Notice the if-else statement in my program. The loop will only run IF the user inputs a positive number. Otherwise, the user will just see a message that goes Need a 0 or a positive number. I decided to include the if-else statement since Fibonacci sequences don’t have any negative numbers.

Let’s see some sample output:

run:
Please choose a number:
112
0 + 1 + 1 + 2 + 3 + 5 + 8 + 13 + 21 + 34 + 55 + 89 + BUILD SUCCESSFUL (total time: 6 seconds)

run:
Please choose a number:
-5
Need a 0 or a positive number
BUILD SUCCESSFUL (total time: 3 seconds)

As you can see, my first output-112-displays the Fibonacci sequence up to 112 while my second output-negative 5-displays a message that is shown when a negative number is chosen.

Here is the code for my next program (video in link)-Factorial program:

package javalessons;
import java.util.Scanner;

public class JavaLessons
{

public static void main(String[] args)
{
Scanner sc = new Scanner (System.in);
System.out.println(“Please choose a number: “);
int num = sc.nextInt();

long factorial = 1;

if (num >= 1)
{
for(int i = 1; i <= num; ++i)
{
factorial *= i;
}
System.out.println(“The factorial of ” + num + ” is ” + factorial);
}

else
{
System.out.println (“Number is too low”);
}
}
}

This program calculates the factorial of a number greater than 0. For those wondering, a factorial is the product of a positive number and all positive numbers below it (stopping at 1). For instance 3 factorial is 6, since 3*2*1=6. Just so you guys know, factorials are denoted by the exclamation point (!), so 3 factorial is 3!.

I have three conditional statements in this program that account for the three possible scenarios of user input (>0,0, and <0). If the user enters a number greater than 0, then the for loop will execute and the factorial of the number will be calculated. If the user enters 0, then the message The factorial of 0 is 1 will be displayed, since 0!=1. If the user enters a negative number, then the message Number is too low will be displayed, since factorials only involve positive numbers.

• If you are wondering why I used long for the factorial variable, I thought it would be more appropriate since factorials can get pretty long (13! is over 6 billion), and long has a wider range than int (9 quintillion as opposed to 2 billion).

Now, let’s see some sample output

run:
Please choose a number:
11
The factorial of 11 is 39916800
BUILD SUCCESSFUL (total time: 12 seconds)

run:
Please choose a number:
0
The factorial of 0 is 1
BUILD SUCCESSFUL (total time: 3 seconds)

run:
Please choose a number:
-14
Number is too low
BUILD SUCCESSFUL (total time: 3 seconds)

run:
Please choose a number:
344
The factorial of 344 is 0
BUILD SUCCESSFUL (total time: 3 seconds)

In the first output sample, I chose 11 and got 39,916,800 as the factorial (11!=39,916,800). In the second output sample, I chose 0 and got 1 as the factorial (remember than 0! is 1). In the third output sample, I chose -14 and got the Number is too low message since factorials only involve positive integers.

Now I know I mentioned that there were three possible scenarios for this program. There are actually 4. See, if you type in a number like 700 or 344 (as I did above), you will get 0 as the factorial, even though the actual factorial will be considerably larger. A 0 will be displayed if the actual factorial is greater than 9 quintillion since long doesn’t extend past 9 quintillion.

This concludes my current series of Java posts, but don’t worry, there will be more Java lessons soon! In the meantime, you can look forward to more R posts.

Thanks for reading,

Michael