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Prime Number Program in Java

A prime number is a number greater than 1 and divided by 1 or by itself. That is, you cannot divide a prime number by any number other than 1 or itself. For example, 2, 3, 5, 7, 11, 13, 17, … etc.

Example – Prime numbers between a given range

public class PrimeNumber {
  public static void main(String[] args) {
    
    int first = 0;
    int last = 50;
    System.out.println("Number of prime numbers between range " + first + " and " + last);

    for (int i = first; i <= last; i++) {
      if (isPrime(i)) {
        System.out.print(i + " ");
      }
    }
  }

  public static boolean isPrime(int n) {
    if (n <= 1) {
      return false;
    }

    for (int i = 2; i <= Math.sqrt(n); i++) {
      if (n % i == 0) {
        return false;
      }
    }
    return true;
  }
}

Output

Number of prime numbers between range 0 and 50
2 3 5 7 11 13 17 19 23 29 31 37 41 43 47

Example – Check if a given number is prime or not using for loop

public class PrimeNumberCheker {

  public static void main(String[] args) {

    int number = 15;
    boolean flag = false;
    for (int i = 2; i <= number / 2; ++i) {
      // condition for nonprime number
      if (number % i == 0) {
        flag = true;
        break;
      }
    }

    if (!flag) {
      System.out.println(number + " is a prime number.");
    } else {
      System.out.println(number + " is not a prime number.");
    }
  }
}

Output

15 is not a prime number.

Example – Print all prime numbers in a given range using for loop

public class PrimeNumberCheker {

  public static void main(String[] args) {

   for(int number=2; number<=50; number++){ // 2 to 50 range
    boolean flag = false;

    for (int i = 2; i <= number / 2; ++i) {
      // condition for nonprime number
      if (number % i == 0) {
        flag = true;
        break;
      }
    }

    if (!flag) {
      System.out.println(number + " is a prime number.");
    } else {
      System.out.println(number + " is not a prime number.");
    }
   }
  }
}

Output

2 is a prime number.
3 is a prime number.
4 is not a prime number.
5 is a prime number.
6 is not a prime number.
7 is a prime number.
8 is not a prime number.
9 is not a prime number.
10 is not a prime number.
11 is a prime number.
12 is not a prime number.
13 is a prime number.
14 is not a prime number.
15 is not a prime number.
16 is not a prime number.
17 is a prime number.
18 is not a prime number.
19 is a prime number.
20 is not a prime number.
21 is not a prime number.
22 is not a prime number.
23 is a prime number.
24 is not a prime number.
25 is not a prime number.
26 is not a prime number.
27 is not a prime number.
28 is not a prime number.
29 is a prime number.
30 is not a prime number.
31 is a prime number.
32 is not a prime number.
33 is not a prime number.
34 is not a prime number.
35 is not a prime number.
36 is not a prime number.
37 is a prime number.
38 is not a prime number.
39 is not a prime number.
40 is not a prime number.
41 is a prime number.
42 is not a prime number.
43 is a prime number.
44 is not a prime number.
45 is not a prime number.
46 is not a prime number.
47 is a prime number.
48 is not a prime number.
49 is not a prime number.
50 is not a prime number.

Example – Check if a given number is prime or not using while loop

public class PrimeNumberCheker {

  public static void main(String[] args) {

    int number = 13; //Given Number
    int i = 2;
    boolean flag = false;
    while (i <= number / 2) {
      
      if (number % i == 0) {
        flag = true;
        break;
      }

      i=i+1;
    }

    if (!flag) {
      System.out.println(number + " is a prime number.");
    } else {
      System.out.println(number + " is not a prime number.");
    }
  }
}

Output

13 is a prime number.
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