Question

Using Java

Prime numbers. Write a program that prompts the user for an integer and then prints out all prime numbers up to that integer. For example, when the user enters 20, the program should print 2 3 5 7 11 13 17 19 Recall that a number is a prime number if it is not divisible by any number except 1 and itself. Use a class PrimeGenerator with methods nextPrime and isPrime. Supply a class PrimePrinter whose main method reads a user input, constructs a PrimeGenerator object, and prints the primes. Submit the Java file and screenshot of the output in zip file.

Answer 1

package october;

import java.util.Scanner;

public class PrimeGenerator {
   //class variables
   private int limit; //will store the limit till when primes are to be generated
   private int start = 2; // will start from 2
  
   //constructor to initialise
   public PrimeGenerator(int limit) {
       this.limit = limit;
   }
  
   //method to print all the primes
   public void printPrimes() {
       System.out.println("The primes upto " + limit + " are: ");
      
       //loop will iterate until lower limit is less than upper limit
       while(start <= limit){
           //this willl get the immediate next prime.
           int p = nextPrime();   
           System.out.print(p + " ");
       }
   }
  
   //this ,ethod will give the next prime
   private int nextPrime() {
       //if start > limit then exit the program
       if(start > limit){
           System.exit(0);
       }
       //checking if start is prime or not
       if(isPrime(start) > 0) {
           //inc. start for the next iteration
           start++;
           return start-1;
       }
       else {
           //if start is not prime
           //inc. it by 1
           start++;
           //calulating the next prime
           return nextPrime();
       }
   }
  
   //method to check whether i is prime or not
   private int isPrime(int i) {
       if(i == 2) return i;
       if(i == 3) return i;
      
       for(int j = 2 ; j <= Math.sqrt(i) ; j++){
           if(i % j == 0) return 0;
       }
       return i;
   }
  
   public static void main(String[] args) {
       System.out.println("Enter the number till you want prime numbers: ");
       Scanner sc = new Scanner(System.in);
      
       int n = sc.nextInt();
       PrimeGenerator pg = new PrimeGenerator(n);
       pg.printPrimes();
       sc.close();
   }
  
}

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