# 1. Introduction

A prime number is a natural number greater than 1 that has no positive divisors other than 1 and itself. Checking if a number is prime is common in programming and mathematics. This blog post will guide you through writing a Java program that determines whether a given number is prime.

# 2. Program Steps

1. Import the Scanner class to read the user's input.

2. Prompt the user to enter a number.

3. Check if the number is prime using a loop.

4. Display the result.

5. Close the Scanner object to prevent resource leaks.

# 3. Code Program

```
import java.util.Scanner;
public class PrimeNumberCheck {
public static void main(String[] args) {
// Creating a Scanner object for reading input
Scanner scanner = new Scanner(System.in);
System.out.println("Enter a number:");
int num = scanner.nextInt();
// Closing the scanner
scanner.close();
// Checking if the number is prime
boolean isPrime = true;
if (num < 2) {
isPrime = false;
} else {
for (int i = 2; i <= num / 2; i++) {
if (num % i == 0) {
isPrime = false;
break;
}
}
}
// Displaying the result
if (isPrime) {
System.out.println(num + " is a prime number.");
} else {
System.out.println(num + " is not a prime number.");
}
}
}
```

### Output:

Enter a number: 17 17 is a prime number. Enter a number: 20 20 is not a prime number.

### Explanation:

1. The program starts by importing the *Scanner* class to read a number input by the user.

2. It prompts the user to enter a number, which is stored in the variable *num*.

3. To determine if *num* is prime, the program initially assumes that *num* is a prime number by setting *isPrime* to true. It then checks if *num* is less than 2, setting *isPrime* to false for numbers less than 2, as they cannot be prime.

4. For numbers 2 and above, the program iterates from 2 to *num / 2*. If *num* is divisible by any number in this range (i.e., *num % i == 0*), it is not prime, and *isPrime* is set to false.

5. After the loop, the program checks the value of *isPrime*. If it remains true, *num* is prime, and the program prints that *num* is a prime number. Otherwise, it prints that *num* is not a prime number.

6. Finally, the Scanner object is closed to prevent resource leaks, following good programming practices.

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