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Prime Number Program in Java

 Prime number in Java: Prime number is a number that is greater than 1 and divided by 1 or itself only. In other words, prime numbers can't be divided by other numbers than itself or 1. For example 2, 3, 5, 7, 11, 13, 17.... are the prime numbers.

Note: 0 and 1 are not prime numbers. The 2 is the only even prime number because all the other even numbers can be divided by 2.

Let's see the prime number program in java. In this java program, we will take a number variable and check whether the number is prime or not.

  1. public class PrimeExample{    
  2.  public static void main(String args[]){    
  3.   int i,m=0,flag=0;      
  4.   int n=3;//it is the number to be checked    
  5.   m=n/2;      
  6.   if(n==0||n==1){  
  7.    System.out.println(n+" is not prime number");      
  8.   }else{  
  9.    for(i=2;i<=m;i++){      
  10.     if(n%i==0){      
  11.      System.out.println(n+" is not prime number");      
  12.      flag=1;      
  13.      break;      
  14.     }      
  15.    }      
  16.    if(flag==0)  { System.out.println(n+" is prime number"); }  
  17.   }//end of else  
  18. }    
  19. }   
Test it Now

Output:

3 is prime number

Prime Number Program using Method in Java

  1. public class PrimeExample2{    
  2. static void checkPrime(int n){  
  3.   int i,m=0,flag=0;      
  4.   m=n/2;      
  5.   if(n==0||n==1){  
  6.    System.out.println(n+" is not prime number");      
  7.   }else{  
  8.    for(i=2;i<=m;i++){      
  9.     if(n%i==0){      
  10.      System.out.println(n+" is not prime number");      
  11.      flag=1;      
  12.      break;      
  13.     }      
  14.    }      
  15.    if(flag==0)  { System.out.println(n+" is prime number"); }  
  16.   }//end of else  
  17. }  
  18.  public static void main(String args[]){    
  19.   checkPrime(1);  
  20.   checkPrime(3);  
  21.   checkPrime(17);  
  22.   checkPrime(20);  
  23. }    
  24. }   
Test it Now

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.

  1. import java.util.Scanner;  
  2.   
  3. import java.util.Scanner;  
  4.   
  5. public class PrimeExample3 {  
  6.   
  7.    public static void main(String[] args) {  
  8.        Scanner s = new Scanner(System.in);  
  9.        System.out.print("Enter a number : ");  
  10.        int n = s.nextInt();  
  11.        if (isPrime(n)) {  
  12.            System.out.println(n + " is a prime number");  
  13.        } else {  
  14.            System.out.println(n + " is not a prime number");  
  15.        }  
  16.    }  
  17.   
  18.    public static boolean isPrime(int n) {  
  19.        if (n <= 1) {  
  20.            return false;  
  21.        }  
  22.        for (int i = 2; i < Math.sqrt(n); i++) {  
  23.            if (n % i == 0) {  
  24.                return false;  
  25.            }  
  26.        }  
  27.        return true;  
  28.    }  
  29. }  

Output:

Use image PrimeExample1

Find prime numbers between two numbers

You can also find prime numbers between two specified numbers.

  1. import java.util.Scanner;  
  2. public class PrimeExample4 {  
  3.    public static void main(String[] args) {  
  4.        Scanner s = new Scanner(System.in);  
  5.        System.out.print("Enter the first number : ");  
  6.        int start = s.nextInt();  
  7.        System.out.print("Enter the second number : ");  
  8.        int end = s.nextInt();  
  9.        System.out.println("List of prime numbers between " + start + " and " + end);  
  10.        for (int i = start; i <= end; i++) {  
  11.            if (isPrime(i)) {  
  12.                System.out.println(i);  
  13.            }  
  14.        }  
  15.    }  
  16.    public static boolean isPrime(int n) {  
  17.        if (n <= 1) {  
  18.            return false;  
  19.        }  
  20.        for (int i = 2; i <= Math.sqrt(n); i++) {  
  21.            if (n % i == 0) {  
  22.                return false;  
  23.            }  
  24.        }  
  25.        return true;  
  26.    }  
  27. }  
  28.    

Output:

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