Write a program in java to enter two numbers and check if they are twin prime numbers or not.
Twin Primes are the prime numbers with a
difference of 2, e.g., (3, 5), (5, 7), (11, 13), (17, 19), (29, 31) ... etc.
In this
program isPrime(int n) will return true if the number is prime and false if it
is not prime. This method is called in the main() method which checks the numbers
are prime or not and also the difference between two prime numbers is 2. And if
it is then it called Twin prime number.
Solution
import java.io.*;
// Program to check twin prime
public class TwinPrimeNumber
{
public static boolean
isPrime(int n)
{
// boolean value will
return
boolean f = true;
for (int i = 2; i
<= n / 2; i++) {
if (n % i == 0) {
f = false;
break;
}
}
return f;
}
// main method begins
public static void
main(String args[]) throws IOException
{
int number1, number2;
// InputStreamReader
object
InputStreamReader in
= new InputStreamReader(System.in);
// BufferedReader
object
BufferedReader br =
new BufferedReader(in);
System.out.print("Enter first number: ");
// First number
number1 =
Integer.parseInt(br.readLine());
System.out.print("Enter second number: ");
// Second number
number2 =
Integer.parseInt(br.readLine());
// Checking both the number is prime and the difference between two is 2
if (isPrime(number1)
== true && isPrime(number2) == true && Math.abs(number2 -
number1) == 2) {
System.out.println("Twin prime number");
} else {
System.out.println("Not twin prime numbers");
}
} // end method main
} // end class
Output
Enter first number: 11
Enter second number: 13
Twin prime number
Enter first number: 9
Enter second number: 11
Not twin prime numbers
In the above program, a method public static boolean isPrime(int n) is used to check prime numbers. This method return a boolean value. If the number is prime then it will send true otherwise false. In main() method isPrime called two times to check true or false.
//Twin prime number without method
import java.util.*;
public class TwinPrime
{
public static void main(String args[])
{
int n1, n2, i, f1,f2;
f1=f2=1;
Scanner sc=new Scanner(System.in);
System.out.println("Enter First number:");
n1=sc.nextInt();
System.out.println("Enter Second number:");
n2=sc.nextInt();
for(i=2; i<n1; i++)
{
if(n1%i==0)
{
f1=0;
break;
}
}
for(i=2; i<n2; i++)
{
if(n2%i==0)
{
f2=0;
break;
}
}
if(f1==1 && f2==1 && Math.abs(n1-n2)==2)
{
System.out.println("Twin Prime Number");
}
else
{
System.out.println("Not a Twin Prime Number");
}
}
}
