# Recursive Fibonacci Sequence in Java

## Fibonacci Sequence

A sequence that is formed by the addition of the last two numbers starting from 0 and 1. If one wants to find the nth element, then the number is found by the addition of (n-1) and (n-2) terms, where n must be greater than 0.

## Recursion

Recursion is the process where the same definitive function or procedure calls itself multiple times until it encounters a terminating condition. If we do not specify a terminating condition, the method will enter into an infinite loop state.

## Recursive Fibonacci Sequence in Java

In the code given below, the `main()` method calls a static function `getFibonacciNumberAt()` defined in the class. The function takes a parameter that defines a number, where we want to evaluate the Fibonacci number. The function has a primary check that will return 0 or 1 when it meets the desired condition. Otherwise, the function will again call itself by decrementing the parameter passed to it.

``````package recursiveFibonacci;

public class RecursiveFibonacciSequence {
public static void main(String[] args) {
int fibonacciNumber = getFibonacciNumberAt(6);
System.out.println(fibonacciNumber);
}

public static int getFibonacciNumberAt(int n) {
if (n == 0)
return 0;
else if (n == 1)
return 1;
else
return getFibonacciNumberAt(n - 1) + getFibonacciNumberAt(n - 2);
}
}
``````

Output:

``````8
``````

The detailed evaluation can be seen below :

``````getFibonacciNumberAt(6) = getFibonacciNumberAt(5) + getFibonacciNumberAt(4); //5+3=8
getFibonacciNumberAt(5) = getFibonacciNumberAt(4) + getFibonacciNumberAt(3); //3+2=5
getFibonacciNumberAt(4) = getFibonacciNumberAt(3) + getFibonacciNumberAt(2); //2+1=3
getFibonacciNumberAt(3) = getFibonacciNumberAt(2) + getFibonacciNumberAt(1); //1+1=2
getFibonacciNumberAt(2) = getFibonacciNumberAt(1) + getFibonacciNumberAt(0); //1+0=1
If, getFibonacciNumberAt(1) = 1;
And getFibonacciNumberAt(0) = 0;
``````

We can modify the above program to print a series up to the desired number.

``````package recursiveFibonacci;

public class RecursiveFibonacci {
public static void main(String[] args) {
int maxCount = 10;
for (int i = 0; i <= maxCount; i++) {
int fibonacciNumber = printFibonacci(i);
System.out.print(" " + fibonacciNumber);
}
}

public static int printFibonacci(int n) {
if (n == 0)
return 0;
else if (n == 1)
return 1;
else
return printFibonacci(n - 1) + printFibonacci(n - 2);
}
}
``````

Output:

``````0 1 1 2 3 5 8 13 21 34 55
``````
Note

For calculation of larger numbers, we can use the `BigInteger` class in Java. The recursion process will be complex for larger numbers; hence the computation time for such numbers will also be more.

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