Prime Number Program in Java

In Java, a prime number refers to a number greater than 1 that can only be divided evenly by 1 and itself. In other words, prime numbers cannot be divided by any other numbers apart from 1 and the number itself. For instance, 2, 3, 5, 7, 11, 13, 17, and so on, are examples of prime numbers. They possess the unique characteristic of being divisible solely by 1 and the number itself, without any other divisors.

Now, let’s examine a Java program to determine whether a given number is prime or not. In this program, we will define a number variable and subsequently verify its primality.

Program:

public class PrimeExample{    
 public static void main(String args[]){    
  int i,m=0,flag=0;      
  int n=10;//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:

10 is not a prime number

Prime Number Program using Method in Java

public class PrimeExample1{    
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

Find prime numbers between two numbers in Java

You can find prime numbers between two specified numbers.

import java.util.Scanner;  
public class PrimeExample2 {  
   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:

Enter the first number : 1
Enter the second number : 2
List of prime numbers between 1 and 2
2

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