import java.util.Scanner;
public class PrimeNumberChecker {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
System.out.print("Enter a number: ");
int number = scanner.nextInt();
if (isPrime(number)) {
System.out.println(number + " is a prime number.");
} else {
System.out.println(number + " is not a prime number.");
}
scanner.close();
}
public static boolean isPrime(int num) {
if (num <= 1) {
return false; // Numbers less than or equal to 1 are not prime
}
// Check divisibility from 2 to the square root of the number
for (int i = 2; i <= Math.sqrt(num); i++) {
if (num % i == 0) {
return false; // If divisible by any number between 2 and sqrt(num), not prime
}
}
return true; // If no divisors found, it's a prime number
}
}
(code-box)
Explanation:
1. The program starts by importing the `Scanner` class from the `java.util` package, which is used to read user input.
2. In the `main` method, the user is prompted to enter a number.
3. The `isPrime` method is defined to check whether a given number is prime. It takes an integer as a parameter.
4. Inside the `isPrime` method, the first check is whether the number is less than or equal to 1. Prime numbers are greater than 1, so any number less than or equal to 1 is not prime.
5. Next, a loop iterates from 2 to the square root of the number. This is an optimization, as factors of a number are typically found in the range from 2 to the square root of the number.
6. In the loop, the program checks if the number is divisible by the current value of `i`. If it is, then the number is not prime (since a prime number has only two divisors: 1 and itself).
7. If the loop completes without finding any divisors, the program concludes that the number is prime.
8. Back in the `main` method, the `isPrime` function is called with the user's input number. Depending on the return value, the program prints whether the number is prime or not.
9. Finally, the `Scanner` is closed to release the system resources.
This program checks whether the given number is prime by testing its divisibility against numbers from 2 up to the square root of the number. If the number has no divisors within this range, it is considered prime.
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