Sum of First n Prime Numbers in Java

In this tutorial, we will be heading towards writing the Java program to find the Sum of first n Prime numbers.

Before moving towards actually writing code first, let’s understand what is a prime number.
A Prime number is a natural number that is divisible only by itself and 1.

Following are prime numbers starting from 1:
2,3,5,7,11,13,17,19,23,29,……….

Java Program to find out the sum of First n Prime numbers :

import java.util.*;
import java.io.*;
class SumOfPrime
{
  public static void main(String arg[])
  {
    Scanner sc=new Scanner(System.in);
    int n,sum=0,i=1,j;
    n=sc.nextInt();
    int t=n;
    while(n!=0)
    {
      int count=0;
      for(j=1;j<=i;j++)
      {
        if(i%j==0)
        {
          count++;
        }
      }
      if(count==2)
      {
        sum=sum+i;
        n--;
      }
      i++;
    }
    System.out.println("Sum of first "+t+" prime numbers is "+sum);
  }
}

Output:
5
Sum of first 5 prime numbers is 28

The first 5 prime numbers are 2,3,5,7,11.
Sum of first 5 prime number is 2+3+5+7+11 =28

The logic of the program :

For the above problem statement, we have to first find a prime number starting from 1, In-Line 14 to 20, we are finding a divisor of number starting from 1 (In this case we are checking whether i=1 is prime or not). Inline 21 we are checking if the number has only two divisors then it is a prime number. If we got any prime number then add this number in the value of a variable sum (In this case we add 1 value to sum value 0). Also, we reduce the value of n by 1 (Since we got the first prime number).

Description of each line of the above program :

Line 1 and 2 denote the importing (including) of packages (folder).
Line 3 denotes the creation of a class with keyword “class” and the class name is “SumOfPrime”.
Line 4 denotes the starting of a class by using opening curly braces ” { “
Line 5 denotes the main method. It includes the method signature of the main method.
Line 6 denotes the starting of the main method by using opening curly braces ” { “.
Line 7 denotes the scanner class which is an inbuilt class in java. It is used to take input from a user. By using the object of Scanner class which is (sc) we can take input from the user.
Line 8 denotes the declaring of variables n, sum, i and j. And we also initialize some variables among them. (sum=0 and i=1).
Line 9 denotes the taking of input from a user by using the nextInt() method.
Line 10 denotes the creation of a temporary variable (t). In this program, we assign a value of n to a temporary variable(t).

Steps of Finding prime number and adding this prime number to the value of sum variable

Line 11, In this we create the while loop. The condition (n!=0), denotes that control will not come out of this loop till (n!=0). When the condition present in while loop is true then control will come out of the loop.
Line 12 denotes the starting of a while loop by using opening curly braces ” { “
Line 13 denotes the declaration and initialization of variable count to zero. (count=0)
Line 14 denotes the starting of for loop. In this for loop, we initialize variable j to 1 (j=1) and we check the condition that “Is (j<=i)” if a condition is true then control go inside the For loop.
Line 15 denotes the starting of for loop by using opening curly braces ” { “
Line 16 denotes the use of the IF statement. In this we check condition (i%j==0). If a condition is true then control will move inside the loop.
Line 17 denotes the starting of an IF statement by using opening curly braces ” { “
Line 18 denotes the increment of variable count by 1.
Line 19 denotes the closing of if statement.
Line 20 denotes the closing of for loop.
Line 21 denotes using of IF statement to check condition (count==2). If a condition is true then all statements (lines) present in the IF statement are executed.
Line 26 denotes the incrementing the value of the variable i by 1.

Step to print the value of sum variable

Line 28 denotes the printing the “Sum of first n prime numbers ” by using System class.
Line 29 and 30 denote the closing of the “main” method and “SumOfPrime” class.

Also read: How to call non static method from static method in Java