fn = fn-1 + fn-2.

# 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

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.

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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