Prime numbers are the numbers that are divided by 1 or the number itself and cannot be divided by any other number without leaving the remainder.
For example, 17 is a prime number. It is only divided by 1 and cannot be divided by any other number with the remainder of 0.
Here we have 2 methods to check whether a given number is prime or not:
Using For Loop
Using Recursion
Method 1: Using For Loop
import java.util.Scanner;
public class Main
{
public static void main(String[] args)
{
//Take input from the user
//Create instance of the Scanner class
Scanner sc = new Scanner(System.in);
System.out.println("Enter a number : ");
int num = sc.nextInt();
int flag=0;
int i, temp=num/2;
if(num==0||num==1)
{
System.out.println(num+" is not prime number");
}
else
{
for(i=2;i<=temp;i++)
{
if(num%i==0)
{
System.out.println(num+" is not a prime number");
flag=1;
break;
}
}
if(flag==0)
{
System.out.println(num+" is a prime number");
}
}//end of else
}
} Output:
Method 2: Using Recursion
import java.util.Scanner;
public class Main
{
static int i=2;
public static void main(String[] args)
{
//Take input from the user
//Create instance of the Scanner class
Scanner sc = new Scanner(System.in);
System.out.println("Enter the number: ");
int num = sc.nextInt();
if (checkPrime(num))
{
System.out.print(num+" is a prime number ");
}
else
{
System.out.println(num+" is not a prime number ");
}
}
static boolean checkPrime(int num)
{
// Corner cases
if (num == 0 || num == 1)
{
return false;
}
// Checking Prime
if (num == i)
return true;
// Base cases
if (num % i == 0)
{
return false;
}
i++;
return checkPrime(num);
}
} Output:
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