Lecture 77:-  Check for Prime and Next Prime

To check for a prime number and find the next prime number in Java, you can create separate methods for each task. A prime number is a natural number greater than 1 that has no positive divisors other than 1 and itself.

Here's an example of how to do this:

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import java.util.Scanner; public class PrimeNumbers {    public static void main(String[] args) {        Scanner scanner = new Scanner(System.in);        System.out.print("Enter a number: ");        int num = scanner.nextInt();        if (isPrime(num)) {            System.out.println(num + " is a prime number.");        } else {            System.out.println(num + " is not a prime number.");        }        int nextPrime = findNextPrime(num);        System.out.println("Next prime number after " + num + " is " + nextPrime + ".");    }    // Method to check if a number is prime    public static boolean isPrime(int num) {        if (num <= 1) {            return false;        }        for (int i = 2; i <= Math.sqrt(num); i++) {            if (num % i == 0) {                return false;            }        }        return true;    }    // Method to find the next prime number after a given number    public static int findNextPrime(int num) {        int nextNum = num + 1;        while (true) {            if (isPrime(nextNum)) {                return nextNum;            }            nextNum++;        }    } }

In this example, we have two methods: isPrime() to check if a number is prime and findNextPrime() to find the next prime number after a given number.

1. isPrime(int num):
   • This method takes an integer num as input and returns a boolean value indicating whether the number is prime or not.
   • It first checks if the number is less than or equal to 1; in such cases, the number is not prime.
   • It then iterates from 2 up to the square root of num and checks if any of these numbers divide num without leaving a remainder. If any such divisor is found, the number is not prime.
   • If no divisors are found, the number is prime.
2. findNextPrime(int num):
   • This method takes an integer num as input and returns the next prime number after num.
   • It starts by initializing nextNum to num + 1.
   • It then repeatedly checks if nextNum is prime using the isPrime() method. If it is prime, it returns nextNum; otherwise, it increments nextNum and repeats the process.

By using these methods, you can easily check if a number is prime and find the next prime number in Java.