basic-programs/java/PrimeCheck.java at master · Skm26/basic-programs · GitHub

43 lines (37 loc) · 1.6 KB

import java.util.InputMismatchException;

import java.util.Scanner;

/**

* To check whether a given number is prime

public class PrimeCheck {

public static void main(String[] args) {

// Accept input from the console

System.out.print("Please enter a natural number: ");

int num = 0;

try {

Scanner sc = new Scanner(System.in);

num = sc.nextInt();

sc.close();

} catch (InputMismatchException e) {

outputAndEnd("Input not valid, expected a natural number."); // Error message for all non numerical inputs

}

if (num < 0) {

outputAndEnd("Input not valid, natural number expected"); // Error message for all negative inputs

} else if (num < 2) {

outputAndEnd("0 and 1 are neither prime nor composite"); // Info message for 0 and 1

}

// Check if the given number is divisible from any number between 2 and num/2, if so, its composite

for (int i = 2; i <= num / 2; i++) {

if (num % i == 0) {

outputAndEnd(num + " is not a prime number."); // Output result and exit as we found one divisor other than 1 and itself

}

// The number has exit the loop with no divisors, which means it is a prime number, print success message.

outputAndEnd(num + " is a prime number.");

}

// A method to print the given message and exit the program

private static void outputAndEnd(String message) {

System.out.println(message); // output the given message

System.exit(0); // exit the program

}

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