Java Program to check whether a number is prime or notPrime

 prime 

A number is said to be a prime number if and only if it is divisible by 1 and the number itself. So in order to check whether a number n is Prime or not Prime we have to check condition till n-1 . To make it simple if the number is 6 then we will check from 2 till 5 and see if it's divisible by any number and if it's not divisible by any number then it is prime. 6 is divisible by 3 so 6 is not a prime. we can just see and tell 6 is not a prime number but we can't do that for numbers>100 or >1000 as fast as compiler does.

a)Java Program to check  a given number is prime or not

import java.util.Scanner;
  public class prime{
  public static void main(String args[]){
       int flag=0;
       //Scanner sc=new Scanner(System.in);
       //int n=sc.nextInt(); //if n is user input
       int n=127;
       for(int i=2;i<n;i++){
        if(n%i==0){
               flag=1;
               break;
         }
        }
        if(flag==0){
           System.out.println("Prime Number");
         }
         else{
           System.out.println("Not Prime");
         }
       }
    }
       
         
       

Output:"Prime Number"

b)Java Program to print prime numbers between a range of numbers

import java.util.Scanner;
  public class prime{
  public static void main(String args[]){
       Scanner sc=new Scanner(System.in);
       int n=sc.nextInt(); 
       int m=sc.nextInt();
        for(int i=n;i<=m;i++){
           int flag=0;
           for(int j=2;j<i;j++){
             if(i%j==0){
                 flag=1;
               }
            }
            if(flag==0){
               System.out.print(i+" ");
            }
          }
   
       }
    }
       
         
       

Output:

3 ---(n entered by user)

20---(m entered by user)

3 5 7 11 13 17 19 --(prime numbers between 3 and 20)