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Thread: Prime Number Algorithm in Java

  1. #1
    Junior Member arjunkumar's Avatar
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    Prime Number Algorithm in Java



    Hello All, I want to know prime number algorithms. If I have 1 to 100 number how I can find the prime number in scanner? Can anyone know about it, If yes then please tell me how to identify the prime number program in java. I have checked some references to get a program of scanner but i didn't an example.

  2. #2
    Junior Member vijaykhatri96's Avatar
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    Is this useful / helpfull? Yes | No
    Hi Arjun,

    It is very simple program, Before starting the logic of the prime number program, you must need to know that what is prime number?
    A prime number 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.

    The number that is divisible by one or by themselves is known as a prime number.

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    Now about the program using Ja
    import java.util.Scanner;
    class PrimeNumbers2
    {
    public static void main (String[] args)
    {
    Scanner scanner = new Scanner(System.in);
    int i =0;
    int num =0;
    String primeNumbers = "";
    System.out.println("Enter a number:");
    int n = scanner.nextInt();
    scanner.close();
    for (i = 1; i <= n; i++)
    {
    int counter=0;
    for(num =i; num>=1; num--)
    {
    if(i%num==0)
    {
    counter = counter + 1;
    }
    }
    if (counter ==2)
    {
    primeNumbers = primeNumbers + i + " ";
    }
    }
    System.out.println("Prime numbers between 1 and n are:"/n);
    System.out.println(primeNumbers);
    }
    }

    To know more and deeper dive about the code running functionality, Checkout this blog post.

  3. #3
    Member punjabdentistry's Avatar
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    Is this useful / helpfull? Yes | No
    Prime Number algorithm Java

    import java.util.*;
    import java.lang.*;

    class primenumber {

    //check for number prime or not
    static boolean isPrime(int n) {
    //check if n is a multiple of 2
    if (n%2==0) return false;
    //if not, then just check the odds
    for(int i=3;i<=Math.sqrt(n);i+=2) {
    if(n%i==0)
    return false;
    }
    return true;
    }
    public static void main(String[] args)
    {
    if(isPrime(19))
    System.out.println(" true") ;

    else
    System.out.println(" false");

    }
    }

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