Java – Fibonacci Series

Fibonacci series is a series of numbers in which at any point an element is equal to the sum of its previous immediate two terms. The first two terms are zero and 1.

In this tutorial, we learn to write Java programs that print Fibonacci series using different looping techniques.

Fibonacci Series using For Loop

In this example, we shall use Java For Loop to generate an array with given number of terms of Fibonacci series.

Java Program

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/**
 * Java Program - Fibonacci
 * 0 1 1 2 3 5 8 13 21 34 55 . .
 */

public class Fibonacci {

	public static void main(String[] args) {

		int nterms = 10;
		
		int[] fibo = new int[nterms];
		
		for (int index=0; index < fibo.length; index++) {
			if(index==0) {
				fibo[index] = 0;
			} else if(index==1) {
				fibo[index] = 1;
			} else {
				fibo[index] = fibo[index-1] + fibo[index-2]; 
			}
		}
		
		//print fibonacci series
		for(int n:fibo)
			System.out.print(n+"  ");
		
	}

}

Output

0  1  1  2  3  5  8  13  21  34

Algorithm to print Fibonacci series of n terms

We shall use the following algorithm to print Fibonacci series of n terms. You can use while loop or for loop to realize this algorithm.

  1. Start.
  2. Get the value of n in a variable nTerms. We shall generate first n terms in Fibonacci series.
  3. Take two variables n1 and n2. Initialize these with 0 and 1 respectively.
  4. Initialize i with 1.
  5. Check if i is less than or equal to nTerms. If false go to step 9.
  6. Print n1.
  7. Compute sum of n1 and n2, and load n1 with n2, and n2 with the sum.
  8. Increment i, and go to step 5.
  9. Stop.

Fibonacci Series using For Loop and Without Array

In this example, we shall use Java For Loop to print given number of terms in a Fibonacci series.

Java Program

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/**
 * Java Program - Fibonacci
 * 0 1 1 2 3 5 8 13 21 34 55 . .
 */

public class Fibonacci {

	public static void main(String[] args) {

		int nTerms = 10; //number of elements in fibonacci sequence
		int n1 = 0, n2 = 1; //previous two elements

		for (int i=1; i <= nTerms; i++) {
			System.out.print(n1 + "  ");

			int n = n1 + n2;
			n1 = n2;
			n2 = n;
		}
	}

}

Output

0  1  1  2  3  5  8  13  21  34

Fibonacci Series using While Loop

In this example, we shall use Java While Loop to print n terms of a Fibonacci series.

Java Program

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/**
 * Java Program - Fibonacci
 * 0 1 1 2 3 5 8 13 21 34 55 . .
 */

public class Fibonacci {

	public static void main(String[] args) {

		int nTerms = 10; //number of elements in fibonacci sequence
		int n1 = 0, n2 = 1; //previous two elements

		int i=1;
		while (i <= nTerms) {
			System.out.print(n1 + "  ");

			int n = n1 + n2;
			n1 = n2;
			n2 = n;

			i++;
		}
	}

}

Output

0  1  1  2  3  5  8  13  21  34

Algorithm to print Fibonacci series with last term less than Given Number

We shall use the following algorithm to print Fibonacci series with last term less than a given maximum limit. You can use while loop or for loop to realize this algorithm.

  1. Start.
  2. Get the value of maximum limit of Fibonacci term in a variable max.
  3. Take two variables n1 and n2. Initialize these with 0 and 1 respectively.
  4. Initialize i with 1.
  5. Check if n1 is less than max. If false go to step 9.
  6. Print n1.
  7. Compute sum of n1 and n2, and load n1 with n2, and n2 with the sum.
  8. Increment i, and go to step 5.
  9. Stop.

Fibonacci Series with Last Term less than Given Number

In this example, we shall print all the terms of a Fibonacci series whose last term is less than a given maximum limit.

Java Program

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/**
 * Java Program - Fibonacci
 * 0 1 1 2 3 5 8 13 21 34 55 . .
 */

public class Fibonacci {

	public static void main(String[] args) {

		int max = 100; //number of elements in fibonacci sequence
		int n1 = 0, n2 = 1; //previous two elements

		for (int i=1; n1 < max; i++) {
			System.out.print(n1 + "  ");

			int n = n1 + n2;
			n1 = n2;
			n2 = n;
		}
	}

}

Output

0  1  1  2  3  5  8  13  21  34  55  89

Fibonacci Series using For Loop and Reduced Lines of Code

From the previous example, we shall rearrange the code such that, we have fewer lines of code in and around for loop.

Java Program

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/**
 * Java Program - Fibonacci
 * 0 1 1 2 3 5 8 13 21 34 55 . .
 */

public class Fibonacci {

	public static void main(String[] args) {

		int max = 100; //max term in Fibonacci sequence

		for (int n1 = 0, n2 = 1, n; n1 <= max; n=n1+n2, n1=n2, n2=n)
			System.out.print(n1 + "  ");
		
	}

}

Output

0  1  1  2  3  5  8  13  21  34  55  89

Conclusion

In this Java Tutorial, we learned how to write Java Programs using looping statements to generate Fibonacci Series.