A Prime number is a very crucial number that plays an important role in the concept of mathematics and computers. It is a natural number that is greater than 1 and has only 2 factors which are 1 and the number itself. Let’s see the Prime number program in Java.

Don’t know Java Well? No worries, Have a look at our Java Free Course.

## Prime Number Program in Java

Prime number program in Java: A prime number is a number which has only 2 factors, and those are 1 and the number itself. So, if the number is divisible by any other number then it is not a prime number. The smallest Prime number is 2. 1 is not a prime number.

## Example 1: Prime number program in Java using while loop

public class Main { public static void main(String[] args) { int num = 12; // count variable is used to count the number of factors for a given number int count = 0; int i = 1; // for initiating while loop while (i<=num) { if (num%i == 0) { // this condition will check whether the number is divisible or not count = count+1; // counting the factors } i=i+1; } // comparing if the number of factors is equal to 2 or not if (count == 2){ System.out.println (num+" is a prime number"); } else { System.out.println (num+" is not a prime number"); } } }

### The output of the Example 1 will be like this:

## Example 2: Prime number program in Java using for loop

public class Main { public static void main(String[] args) { int num = 11; // count variable is used to count the number of factors for a given number int count = 0; for (int i=1; i<=num; i++) { if (num%i == 0) { // this condition will check whether the number is divisible or not count = count+1; // counting the factors } i=i+1; } // comparing if the number of factors is equal to 2 or not if (count == 2){ System.out.println (num+" is a prime number"); } else { System.out.println (num+" is not a prime number"); } } }

### The output of the Example 2 will be like this:

## Example 3: Prime number program in Java using Method/Functions

public class Main { // Methode declared for checking whether the number is prime or not public static void primeChecker(int num){ // count variable is used to count the number of factors for a given number int count = 0; for (int i=1; i<=num; i++) { if (num%i == 0) { // this condition will check whether the number is divisible or not count = count+1; // counting the factors } i=i+1; } // comparing if the number of factors is equal to 2 or not if (count == 2){ System.out.println (num+" is a prime number"); } else { System.out.println (num+" is not a prime number"); } } public static void main(String[] args) { int num = 17; primeChecker (num); // Method Called } }

### The output of the Example 3 will be like this:

## Example 4: Prime number program in Java using Method/Functions (Another Way)

public class Main { // Methode declared for checking whether the number is prime or not public static boolean primeChecker(int num){ // count variable is used to count the number of factors for a given number int count = 0; for (int i=1; i<=num; i++) { if (num%i == 0) { // this condition will check whether the number is divisible or not count = count+1; // counting the factors } i=i+1; } // comparing if the number of factors is equal to 2 or not if (count == 2){ return true; // return true if the number is prime } else { return false; } } public static void main(String[] args) { int num = 23; if (primeChecker (num)) { System.out.println (num+" is a prime number"); } else { System.out.println (num+" is not a prime number"); } } }

### The output of the Example 4 will be like this:

## Conclusion

One of the most important programs in Java is the Prime number program in Java. In this article, 4 different ways have been demonstrated for the same program and those are withe while loops, for loops, with user-defined functions.