Prime Number Program in Java

public class PrimeExample{    
 public static void main(String args[]){    
  int i,m=0,flag=0;      
  int n=3;//it is the number to be checked    
  m=n/2;      
  if(n==0||n==1){  
   System.out.println(n+" is not prime number");      
  }else{  
   for(i=2;i<=m;i++){      
    if(n%i==0){      
     System.out.println(n+" is not prime number");      
     flag=1;      
     break;      
    }      
   }      
   if(flag==0)  { System.out.println(n+" is prime number"); }  
  }//end of else  
}    
}   

Output:

3 is prime number

Prime Number Program using Method in Java

public class PrimeExample2{    
static void checkPrime(int n){  
  int i,m=0,flag=0;      
  m=n/2;      
  if(n==0||n==1){  
   System.out.println(n+" is not prime number");      
  }else{  
   for(i=2;i<=m;i++){      
    if(n%i==0){      
     System.out.println(n+" is not prime number");      
     flag=1;      
     break;      
    }      
   }      
   if(flag==0)  { System.out.println(n+" is prime number"); }  
  }//end of else  
}  
 public static void main(String args[]){    
  checkPrime(1);  
  checkPrime(3);  
  checkPrime(17);  
  checkPrime(20);  
}    
}   

Output:

1 is not prime number
3 is prime number
17 is prime number
20 is not prime number

Prime Number Program in Java (Another way)

You can also use a method where number is not predefined. Here, user has to put the number to check if the number is prime.

import java.util.Scanner;  
  
import java.util.Scanner;  
  
public class PrimeExample3 {  
  
   public static void main(String[] args) {  
       Scanner s = new Scanner(System.in);  
       System.out.print("Enter a number : ");  
       int n = s.nextInt();  
       if (isPrime(n)) {  
           System.out.println(n + " is a prime number");  
       } else {  
           System.out.println(n + " is not a prime number");  
       }  
   }  
  
   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:

Use image PrimeExample1

Find prime numbers between two numbers

You can also find prime numbers between two specified numbers.

import java.util.Scanner;  
public class PrimeExample4 {  
   public static void main(String[] args) {  
       Scanner s = new Scanner(System.in);  
       System.out.print("Enter the first number : ");  
       int start = s.nextInt();  
       System.out.print("Enter the second number : ");  
       int end = s.nextInt();  
       System.out.println("List of prime numbers between " + start + " and " + end);  
       for (int i = start; i <= end; i++) {  
           if (isPrime(i)) {  
               System.out.println(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:

Use image PrimeExample2