Java program code to check prime numbers and find next prime number

Any integer greater than 1 that has only two factors (i.e. 1 and the number itself) is called a prime number. Apart from these two numbers, it has no other positive divisors. For example: 7 = 1 × 7

The following is the algorithm to determine whether a number is prime:

• Get the integer variable A.

• Divide variable A by (A-1 to 2).

• If A is divisible by any value in (A-1 to 2), then it is not prime.

• Otherwise it is a prime number.

Example

The following Java program accepts an integer input by the user, determines whether the given number is a prime number, and prints the next prime number.

import java.util.Scanner;
public class NextNumberisPrime {
   public static int isPrime(int num){
      int prime = 1;
      for(int i = 2; i < num; i++) {
         if((num % i) == 0) {
            prime = 0;
         }
      }
      return num;
   }
   public static int nextPrime(int num) {
      num++;
      for (int i = 2; i < num; i++) {
         if(num%i == 0) {
            num++;
            i=2;
         } else {
            continue;
         }
      }
      return num;
   }
   public static void main(String args[]){
      Scanner sc = new Scanner(System.in);
      System.out.println("Enter a number ::");
      int num = sc.nextInt();
      int result = 0;
      int prime = isPrime(num);
      if (prime == 1) {
         System.out.println(num+" is a prime number");
      } else {
         System.out.println(num+" is not a prime number");
      }
      System.out.println("Next prime number is: "+nextPrime(num));
   }
}

Output

Enter a number ::
25
25 is not a prime number
Next prime number is: 29

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