Prime Number Program in Java Using a Scanner

In Java, a prime number is one that can only be divided by one or by itself and is greater than one. In other words, only one or itself can be used to divide prime integers. Prime numbers include 2, 3, 5, 7, 11, 13, and 17.

One and zero are not prime numbers. The number two is the only even prime number, therefore all other even numbers can be divided by it.

Java Prime Number Search Technique

• Consider entering a number.
• Since two is the lowest prime number, see if the number has a divisor in the range [two, number/2].
• No integer may be entirely split by a factor greater than its own half. The number itself (number/2) must be looped through two times.
• If a divisor can be identified, the provided number is not prime; else, it is.

Example

Let's say that 121 was entered as the value. It is put into the num integer variable.

 Since a number is being divided by both itself and by the number 1, num is now divided by other numbers ranging from 2 to 8 (% returns residual). The message "Number is not prime" is displayed on the screen if the integer is divided by any number between 2 and 8, as its remainder will be 0. Since 121 cannot be divided by 2, but can undoubtedly be divided by 3, which gives a remainder of 0, it cannot be a prime number.

Prime Number Program Algorithm

Step 1: Read the number.

Step 2: x = 1, y = 0

Step 3: Continue until step 5 while ensuring that (x =  num)

Step 4: Set y = y + 1 if (num mod x) equals 0.

Step 5: x  =  x + 1

Step 6: Print "num is prime" if y equals 2.

            Print "num is not prime" if not.

Step 7: Exit

Example 1:

import java.util.Scanner; 
 public class PrimeNumber
 { 
     public static void main(String args[]) 
              { 
                   int n,x,y; 
                   Scanner sc=new Scanner(System.in); 
System.out.println("Enter any Number: "); 
                   n =sc.nextInt(); 
                   x=1; 
                   y=0; 
while(x<= n) 
                       { 
                           if((n%x)==0) 
                              y=y+1; 
                              x++; 
                       } 
                        if(x==2) 
System.out.println(n +" is a prime number"); 
                        else 
System.out.println(n +" is not a prime number"); 
              } 
 }

Output

Enter any Number: 3
3 is not a prime number

Example 2:

Using the is Prime() function, which accepts a number as input and gives true if a number is a prime number and false otherwise, is a viable option.

import java.util.Scanner;
class PrimeNUmber {
    public static void main(String[] args) {
        Scanner sc= new Scanner(System.in);
System.out.println("Enter any number : ");
        int number= sc.nextInt();
        if(isPrime(number)) {
System.out.println(number + " is a prime number");
        }
else{
System.out.println(number + " is not a  prime number");
        }
    }
static  booleanisPrime(int n)
    {
if(n <=1)
        {
            return false;
        }
for(int i=2;i<=n/2;i++)
       {
           if((n%i)==0)
return  false;
       }
       return true;
    }
}

Output

Enter any Number: 2
2 is a prime number

Example 3:

import java.util.Scanner;  
import java.util.Scanner;  
public class PrimeNumber {  
   public static void main(String[] args) {  
       Scanner sc = new Scanner(System.in);  
System.out.print("Enter any 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 booleanisPrime(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 any Number: 11
11 is a prime number

Example 4:

import java.util.Scanner;  
public class PrimeNumber {  
   public static void main(String[] args) {  
       Scanner sc = new Scanner(System.in);  
System.out.print("Enter the 1 stnumber : ");  
       int start = sc.nextInt();  
System.out.print("Enter the 2 ndnumber : ");  
       int end = sc.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 booleanisPrime(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 1 st number: 2
Enter the 2 nd number: 5
List of prime numbers between 2 and 5
2
3
5