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Java program for prime numbers

A prime number is the number which is is  divisible by itself and not by other numbers.

A program to check prime number can be made by using for and while loop combination .

This article contains java program for finding prime number ,write a java program for prime number between 1- 100 ,simple program to find prime factorial of a number in java.

EXAMPLE 1 - program to check whether a number is prime number  or not.
import java.util.*;
public class pr
{
public static void main()
{
Scanner sc=new Scanner(System.in);
System.out.println("enter number");
int num=sc.nextInt();
int d=0;
for(int i=2;i<=num;i++)
{
if(num%i==0)
d++;
}
if(d==0)
System.out.println("it is a prime number");
else
System.out.println("it is not a prime number");
}
}

Output
enter number
23
it is a prime number


A prime factorial of a number is the products of all the prime numbers less than the number.


EXAMPLE 2 - program to get prime factorial of a number
import java.util.*;
public class primorial
{
public static void main()
{
Scanner sc=new Scanner(System.in);
System.out.println("enter a number");
int n=sc.nextInt();
int sum=1;
primorial m=new primorial();
for(int i=2;i<=n;i++)
{
if(m.checkPrime(i)==true)
{
sum=sum*i;
}
}
System.out.println("prime factorial of "+n+" is: "+sum);
}
boolean checkPrime(int a)
{
int d=0;
for(int i=2;i<a;i++)
{
if(a%i==0)
d++;
}
if(d==0)
return true;
else
return false;
}
}

Output
enter a number
23
prime factorial of 23 is : 111546435
EXAMPLE 3-java program to find prime 
numbers between 1 and 100
  

  import java.util.*;

Public class primecheck

{

    public static void main()

    {

        Scanner sc=new Scanner(System.in);

        System.out.println("prime numbers are:");

        primecheck m=new primecheck();

        for(int i=2;i<=100;i++)

        {

            if(m.checkPrime(i)==true)

            {

                System.out.println(i);

            }

        }

    }

    boolean checkPrime(int a)

    {

        int d=0;

        for(int i=2;i<a;i++)

        {

            if(a%i==0)

            d++;

        }

        if(d==0)

        return true;

        else

        return false;

    }

}

  

Output

  

  Prime number are:
3

5

7

11

13

17

19

23

29

31

37

41

43

47

53

59

61

67

71

73

79

83

89

97
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