Java Program for Fibonacci Series

The Fibonacci series is a sequence where each number is the sum of the two preceding numbers.

It usually starts with 0 and 1.

1. Understanding the Problem

Generate Fibonacci series up to a given number of terms.

Terms: 5 → 0 1 1 2 3
Terms: 7 → 0 1 1 2 3 5 8

2. Using Basic Loop

              
            
Java

            import java.util.Scanner;

public class FibonacciSeries {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter number of terms: ");
        int n = sc.nextInt();

        int a = 0, b = 1;

        System.out.print("Fibonacci Series: ");

        for (int i = 1; i <= n; i++) {
            System.out.print(a + " ");
            int next = a + b;
            a = b;
            b = next;
        }
    }
}
          

3. Optimized Approach (Using Recursion)

              
            
Java

            import java.util.Scanner;

public class FibonacciRecursive {

    static int fib(int n) {
        if (n <= 1)
            return n;
        return fib(n - 1) + fib(n - 2);
    }

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter number of terms: ");
        int n = sc.nextInt();

        System.out.print("Fibonacci Series: ");
        for (int i = 0; i < n; i++) {
            System.out.print(fib(i) + " ");
        }
    }
}
          

4. Common Mistakes

1. Incorrect initialization of first two numbers.

2. Using recursion without understanding performance impact.

3. Printing wrong number of terms.

4. Not handling n = 0 or n = 1 properly.

5. Applications

1. Used in algorithm design and dynamic programming.

2. Appears in nature (e.g., leaf arrangement, spirals).

3. Common interview and beginner programming problem.

Conclusion

Fibonacci series is a classic example to understand loops and recursion.

Iterative methods are more efficient than recursion for large inputs.