Fibonacci Series Java Program Using Stream API

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Introduction

The Fibonacci series is a sequence of numbers where each number is the sum of the two preceding ones, usually starting with 0 and 1. In this guide, we'll explore how to generate the Fibonacci series in Java using the Stream API, which was introduced in Java 8.

Problem Statement

Create a Java program that:

• Generates a specified number of Fibonacci numbers.
• Uses the Java 8 Stream API to generate the series.

Example 1:

• Input: 10 (first 10 Fibonacci numbers)
• Output: 0, 1, 1, 2, 3, 5, 8, 13, 21, 34

Example 2:

• Input: 5 (first 5 Fibonacci numbers)
• Output: 0, 1, 1, 2, 3

Solution Steps

1. Create a Stream to Generate Fibonacci Numbers: Use the Stream.iterate method to generate a stream of Fibonacci numbers.
2. Limit the Number of Fibonacci Numbers: Use the limit method to restrict the stream to the desired number of elements.
3. Collect and Print the Series: Collect the Fibonacci numbers into a list and print them.

Java Program

import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;

/**
 * Java Program to Generate Fibonacci Series using Stream API
 * Author: https://www.javaguides.net/
 */
public class FibonacciStream {

    public static void main(String[] args) {
        // Step 1: Define the number of Fibonacci numbers to generate
        int n = 10; // You can change this to generate more or fewer numbers

        // Step 2: Generate the Fibonacci series using Stream API
        List<Integer> fibonacciSeries = Stream.iterate(new int[]{0, 1}, t -> new int[]{t[1], t[0] + t[1]})
                .limit(n)
                .map(t -> t[0])
                .collect(Collectors.toList());

        // Step 3: Output the Fibonacci series
        System.out.println("First " + n + " Fibonacci numbers: " + fibonacciSeries);
    }
}

Explanation

Step 1: Define the Number of Fibonacci Numbers to Generate

• The variable n is set to determine how many Fibonacci numbers you want to generate. For this example, it's set to 10.

Step 2: Generate the Fibonacci Series Using Stream API

• Stream.iterate: This method creates an infinite stream of Fibonacci pairs. The seed is the initial pair [0, 1], and the function passed to iterate generates the next pair by summing the previous two numbers.
  • t -> new int[]{t[1], t[0] + t[1]}: This lambda expression produces the next pair in the Fibonacci sequence.
• limit(n): Limits the stream to the first n elements.
• map(t -> t[0]): Extracts the first element of each pair (which is the actual Fibonacci number).
• collect(Collectors.toList()): Collects the generated Fibonacci numbers into a list.

Step 3: Output the Fibonacci Series

• The program prints the list of Fibonacci numbers.

Output Examples

Example 1:

First 10 Fibonacci numbers: [0, 1, 1, 2, 3, 5, 8, 13, 21, 34]

Example 2:

First 5 Fibonacci numbers: [0, 1, 1, 2, 3]

Conclusion

This Java program demonstrates how to generate the Fibonacci series using the Stream API. By leveraging the power of Stream.iterate, the program creates an infinite stream of Fibonacci numbers, which can be limited and collected as needed. This method is not only concise but also highly readable, making it an excellent choice for generating sequences like the Fibonacci series in Java.

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