Different Methods to find Prime Number in Java

A prime number is a number that is only divisible by one or itself. Some of the prime numbers are 2, 3, 5, 7, 11, 13 etc.

Some of the different methods to find a prime number in Java are given as follows −

Method 1 - Find if a number is prime without using a function

A program that finds if the given number is prime without using a function is given as follow −

Example

 Live Demo

public class Example {    public static void main(String args[]) {       int num = 11, flag=0;       if(num == 0||num == 1) {          System.out.println( num + " is not a prime number");       } else {          for(int i = 2; i <= num/2; i++) {             if(num % i == 0) {                System.out.println( num + " is not prime number");                flag = 1;                break;             }          }          if(flag == 0) {             System.out.println( num + " is a prime number");          }       }    } }

Output

11 is a prime number

Method 2 - Find if a number is prime using a function

A program that finds if the given number is prime using a function is given as follow −

Example

 Live Demo

public class Example {    static int PrimeOrNot(int num) {       int flag = 0;       if(num == 0||num == 1) {          flag = 1;       } else {          for(int i = 2; i <= num/2; i++) {             if(num % i == 0) {                flag = 1;                break;             }          }       }       return flag;    }    public static void main(String args[]) {       int flag, num = 11;       flag = PrimeOrNot(num);       if(flag == 0) {          System.out.println( num + " is a prime number");       } else {          System.out.println( num + " is not a prime number");       }    } }

Output

11 is a prime number