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Java Exercises: Compute the sum of first n given prime numbers

Java Basic: Exercise-232 with Solution

Write a Java program to compute the sum of first n given prime numbers.

Input:

n ( n ≤ 10000). Input 0 to exit the program.

Pictorial Presentation:

Java Basic Exercises: Compute the sum of first n given prime numbers.

Sample Solution:

Java Code:

import java.util.*;
public class Main {
 
        public static void main(String[] args) throws java.io.IOException{
            Scanner scan = new Scanner(System.in);
                int count=0;
                int sum=0;
	System.out.println("Input a number (n<=10000) to compute the sum:");
	int n=scan.nextInt();
                for(int i=2;;i++){
                    if(prime(i)){
                        count++;
                        sum+=i;
	 if(count==n)break;
	    }
	         } 
	System.out.println("Sum of first "+n+" prime numbers:"); 
                System.out.println(sum);
	}				
         public static boolean prime (int n){
                if(n==1)return false;
                for(int i=2;i<=Math.sqrt(n);i++)
                    if(n%i==0)return false;
                return true;
            }
}

Sample Output:

Input a number (n<=10000) to compute the sum:
100
Sum of first 100 prime numbers:
24133

Flowchart:

Flowchart: Compute the sum of first n given prime numbers.

Java Code Editor:

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Previous: Write a Java program to find the difference between the largest integer and the smallest integer which are created by 8 numbers from 0 to 9. The number that can be rearranged shall start with 0 as in 00135668.
Next: Write a Java program that accept a even number (n should be greater than or equal to 4 and less than or equal to 50,000, Goldbach number) from the user and create a combinations that express the given number as a sum of two prime numbers. Print the number of combinations.

What is the difficulty level of this exercise?



Java: Tips of the Day

Array vs ArrayLists:

The main difference between these two is that an Array is of fixed size so once you have created an Array you cannot change it but the ArrayList is not of fixed size. You can create instances of ArrayLists without specifying its size. So if you create such instances of an ArrayList without specifying its size Java will create an instance of an ArrayList of default size.

Once an ArrayList is full it re-sizes itself. In fact, an ArrayList is internally supported by an array. So when an ArrayList is resized it will slow down its performance a bit as the contents of the old Array must be copied to a new Array.

At the same time, it's compulsory to specify the size of an Array directly or indirectly while creating it. And also Arrays can store both primitives and objects while ArrayLists only can store objects.

Ref: https://bit.ly/3o8L2KH