Java Program: Calculate sum of prime numbers with lambda expression

Java Lambda Program: Exercise-21 with Solution

Write a Java program to implement a lambda expression to calculate the sum of all prime numbers in a given range.

Note: A prime number (or a prime) is a natural number greater than 1 that is not a product of two smaller natural numbers. A natural number greater than 1 that is not prime is called a composite number. For example, 5 is prime because the only ways of writing it as a product, 1 × 5 or 5 × 1, involve 5 itself. However, 4 is composite because it is a product (2 × 2) in which both numbers are smaller than 4. Primes are central in number theory because of the fundamental theorem of arithmetic: every natural number greater than 1 is either a prime itself or can be factorized as a product of primes that is unique up to their order.

Sample Solution:

Java Code:

import java.util.stream.IntStream;

 public class Main {
   public static void main(String[] args) {
     int start_prime = 100;
     int end_prime = 200;

     // Calculate the sum of prime numbers using lambda expression
     int sumOfPrimes = IntStream.rangeClosed(start_prime, end_prime)
       .filter(Main::isPrime)
       .sum();
     System.out.println("Sum of prime numbers between " + start_prime + " and " + end_prime + ": " + sumOfPrimes);
   }
   // Lambda expression to check if a number is prime
   public static boolean isPrime(int number) {
     if (number <= 1) {
       return false;
     }
     for (int i = 2; i <= Math.sqrt(number); i++) {
       if (number % i == 0) {
         return false;
       }
     }
     return true;
   }
 }

Sample Output:

Sum of prime numbers between 100 and 200: 3167

Explanation:

In the above exercise,

• The start_prime and end_primevariables define the range of numbers within which we want to calculate the sum of prime numbers.
• The lambda expression Main::isPrime filters out non-prime numbers from the range of numbers.
• The isPrime method is a lambda expression itself, which checks whether a given number is prime or not using a simple algorithm.b.

Flowchart:

Live Demo:

Java Code Editor:

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