Fibonacci Series Program in Java

Fibonacci series in Java | In the Fibonacci series, the next element will be the sum of the previous two elements. The Fibonacci sequence is a series of numbers where a number is found by adding up the two numbers before it. Starting with 0 and 1, the sequence goes 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, and so on…

By definition, the first two numbers in the Fibonacci sequence are either 1 and 1, or 0 and 1, depending on the chosen starting point of the sequence, and each subsequent number is the sum of the previous two.

As a rule, the expression is X_n= X_n-1+ X_n-2

import java.util.Scanner;

public class FibonacciSeries {

   public static void displayFibonacci(int term) {

      // declare variables
      int t1 = 0; // first term
      int t2 = 1; // second term	
      int n; // nth term
      int i = 1; // iterator variable

      while(i <= term) {

         // display ith terms
         System.out.print(t1+"\t");

         // update term values
         n = t1 + t2;
         t1 = t2;
         t2 = n;

         // increase iterator variable
         // value by 1
         i++;
      }
   }

   public static void main(String[] args) {

      int terms; // number of terms

      // Read number of terms to display
      Scanner scan = new Scanner(System.in);
      System.out.print("Enter number of terms: ");
      terms = scan.nextInt();

      // display Fibonacci series
      System.out.println("The Fibonacci series: ");
      displayFibonacci(terms);

      // close Scanner class object
      scan.close();
   }
}

The output for different test-cases:-

Enter number of terms: 7
The Fibonacci series:
0 1 1 2 3 5 8

Enter number of terms: 10
The Fibonacci series:
0 1 1 2 3 5 8 13 21 34

The above Fibonacci series program in Java is developed by using a while loop. We can also use for loop to find the Fibonacci series.

Using for loop

public static void displayFibonacci(int term) {

	int t1 = 0; // first term
	int t2 = 1; // second term	
	int n; // nth term

	for(int i=1; i <= term; i++) {

		// display ith terms
		System.out.print(t1+"\t");

		// update term values
		n = t1 + t2;
		t1 = t2;
		t2 = n;
	}
}

Fibonacci series program in Java up to a given number

We can also display the Fibonacci series up to a given number. In this case, again we can use any looping statement like for loop or while loop or do-while loop.

import java.util.Scanner;

public class FibonacciSeries {

   public static void displayFibonacci(int range) {

      // declare variables
      int t1 = 0; // first term
      int t2 = 1; // second term	
      int n; // nth term

      while(t1 <= range) {

	 //display the term
	 System.out.print(t1+"\t");

	 // update term values
	 n = t1 + t2;
	 t1 = t2;
	 t2 = n;
      }
   }

   public static void main(String[] args) {
      int range; // range value

      // Read range value
      Scanner scan = new Scanner(System.in);
      System.out.print("Enter range: ");
      range = scan.nextInt();

      // display Fibonacci series
      System.out.println("The Fibonacci series"
      		+ " upto "+range+" is: ");
      displayFibonacci(range);

      // close Scanner class object
      scan.close();
   }
}

The output for the different test-cases:-

Enter range: 20
The Fibonacci series up to 20 is:
0 1 1 2 3 5 8 13

Enter range: 100
The Fibonacci series up to 100 is:
0 1 1 2 3 5 8 13 21 34 55 89

Enter range: 1000
The Fibonacci series up to 1000 is:
0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987

Finding Nth Fibonacci term in Java

import java.util.Scanner;

public class FibonacciSeries {

   public static int nthFibonacciTerm(int term) {

      int t1 = 0; // first term
      int t2 = 1; // second term
      int n = 0; // nth term

      if(term==1) return t1;
      if(term==2) return t2;

      // 2 terms are already exist so 
      // iterator variable should 
      // start with 3
      for(int i=3; i <= term; i++) {

         // update term values
         n = t1 + t2;
         t1 = t2;
         t2 = n;
      }

      return n;
   }

   public static void main(String[] args) {

      int n; // range value

      // read range value
      Scanner scan = new Scanner(System.in);
      System.out.print("Enter n value: ");
      n = scan.nextInt();

      // display Fibonacci series
      System.out.println(n+" Fibonacci term "
		+ " is = "+ nthFibonacciTerm(n));

      // close Scanner class object
      scan.close();
   }
}

The output for the different test-cases:-

Enter n value: 1
1 Fibonacci term is = 0

Enter n value: 2
2 Fibonacci term is = 1

Enter n value: 7
7 Fibonacci term is = 8

Enter n value: 10
10 Fibonacci term is = 34

We can also find the Fibonacci series using the recursion technique. For more see:- Fibonacci series using recursion

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