Factorial in Java, Recursively and Non-Recursively

FactorialDemo demonstrates how to implement Factorial problem both recursively and non-recursively in Java.

1:  // Program by Luis Gallego Cardona.   

2:  package com.factorialdemo;
3:  import javax.swing.*;
4:  public class FactorialDemo {
5:       public static void main(String[] args) {
6:            String input; // hold the input
7:            int number; // hold a number
8:            // Get the number from the user
9:            input = JOptionPane.showInputDialog("Enter a non-negative number");
10:            number = Integer.parseInt(input);
11:            // Display the users input
12:            JOptionPane.showMessageDialog(null, number + "! is " + factorial(number) + ", using recursion"); // This shows the factorial using recursion
13:            JOptionPane.showMessageDialog(null, number + "! is " + nonrecursivefactorial(number) + ", not using recursion"); // This shows the factorial NOT using recursion
14:            System.exit(0);  
15:            // NOTE: What is the purpose of System.exit(0)? I know I have to call this whenever I use JOptionPane ... but that's about it.
16:       }
17:       private static int nonrecursivefactorial(int n) {
18:            int x; // this holds the number
19:            int fact = 1; // this is a place holder for the result of the factorial
20:            /** The for loops takes in a number as x, then assigns the value as n, which is the counter in the for loop.  
21:             * it then multiplies the number we passed in by 1 (base case), then it keeps multiplying the new number all the way until n is < 1. Thus breaks the loop
22:             */
23:            for (x = n; x > 1; x--)
24:                 fact *= x;
25:            return fact;
26:       }
27:       private static int factorial(int n) {
28:            if(n == 0)
29:                 return 1; // this is the base case , because 0! = 1
30:            else  
31:                 return n * factorial(n - 1);
32:       }
33:  }

Fibonacci sequence in Java, Recursive and Non-Recursive

This is an example in Java of how to implement the Fibonacci Sequence both recursively and Non-Recursively (or using loops).  Any questions please ask, if you don't understand how a method works, make a table!

1:  // This program is written by Luis Gallego Cardona.  

2:  package com.fibonaccidemo; // Comment out if it gives you issues
3:  import java.util.Scanner;
4:  public class FibonacciDemo {
5:       public static void main(String[] args) {
6:            Scanner keyboard = new Scanner(System.in);
7:            int number = 0;      // hold the number
8:            System.out.print("Please enter the nth term of the Fibonacci: ");
9:            number = keyboard.nextInt();
10:            // Recursive call that prints out each number in the sequence up to the desired nth term.
11:            for (int i = 0; i < number; i++)
12:                 System.out.print(fibonacci(i) + " ");
13:            System.out.println();
14:            // Non-Recursive call that simply prints out the nth term in the sequence.
15:            System.out.print(fibonacciNonRecursive(number) + " ");
16:            keyboard.close();
17:       }
18:       /** fibonacciNonRecursive method
19:        * @param n The nth number to calculate
20:        * @return The nth number.
21:        */
22:       private static int fibonacciNonRecursive(int n) {
23:            if(n == 0)
24:                 return 0;
25:            int x = -1, y = 1, z =0;    
26:            for (int i = 1; i <= n; i++){
27:                 z = x + y ;
28:                 x = y;
29:                 y = z;
30:            }
31:            return y;
32:       }
33:       /**
34:        * The fibonnaci method calculates the nth term in the Fibonnaci series
35:        * @param n The nth number to calculate
36:        * @return The nth number.
37:        */
38:       private static int fibonacci(int n) {
39:                 if (n == 0)
40:                      return 0;
41:                 if (n == 1)
42:                      return 1;
43:                 else
44:                      return fibonacci(n-1) + fibonacci(n-2);
45:       }
46:  }