# Java program for Fibonacci Series

Upasana | August 23, 2022 | 1 min read | 1,015 views

Fibonacci series is series of natural number where next number is equivalent to the sum of previous two number e.g.

Fibonacci Series
`fn = fn-1 + fn-2.`

The first two numbers of Fibonacci series is always 1, 1.

First 10 numbers in fibonacci series are:

`1 1 2 3 5 8 13 21 34 55`

## Iterative approach

Java program to calculate and print Fibonacci number using Iterations logic is shown below:

Basically on each iteration, we are assigning second number to the first and assigning the sum of last two numbers to the second.

Fibonacci using Iteration
``````void fibonacci(int count) {
int prevNumber = 0;
int nextNumber = 1;

System.out.println("Fibonacci Series " + count + ":");
for (int i = 1; i <= count; ++i) {
int fib = prevNumber + nextNumber;
prevNumber = nextNumber;
nextNumber = fib;
System.out.print(prevNumber + " ");
}
}``````

## Recursive approach

We can use tail recursion to calculate fibonacci series in Java.

Tail recursion

A tail recursion is a recursive function where the function calls itself at the end ("tail") of the function in which no computation is done after the return of recursive call.

fibonacci series using Recursion
``````int fibonacci(int num) {
if (num == 1 || num == 2) {
return 1;   (1)
}
return fibonacci(num - 1) + fibonacci(num - 2); (2)
}``````
 1 Terminating condition for recursive function 2 Tail recursion where we are essentially calculating `fn = fn-1 + fn-2`

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