# Java Program to Check if Number is Prime or Not

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In this article, we will write a java program which checks if the number given as input to the Program is Prime Number or Not.

#### Method 1: Simpler to Understand

import java.util.Scanner; public class CheckPrime { public static void main(String args[]) { boolean isPrime=true; Scanner sc= new Scanner(System.in); System.out.println("Enter any number:"); //Take the input from user int num=sc.nextInt(); if(num<=1){ isPrime=false; }else{ for(int i=2;i<num/2+1;i++){ if(num%i==0){ isPrime=false; break; } } //If isPrime is true then the number is prime number else not prime if(isPrime) System.out.println(num + " is a Prime Number"); else System.out.println(num + " is not a Prime Number"); } } }

### Method 2: Optimized Code

import java.util.Scanner; public class CheckPrime { public static void main(String args[]) { boolean isPrime=true; Scanner sc= new Scanner(System.in); System.out.println("Enter any number:"); //Take the input from user int num=sc.nextInt(); int sqrt = (int) Math.sqrt(num) + 1; if(num<=1){ isPrime=false; }else{ // here the loop iterates only upto the square root of the Number. // As all remaining iterations are useless. for(int i=2;i<sqrt;i++){ if(num%i==0){ isPrime=false; break; } } //If isPrime is true then the number is prime number else not prime if(isPrime) System.out.println(num + " is a Prime Number"); else System.out.println(num + " is not a Prime Number"); } } }

### Output:

\$javac CheckPrime.java \$java CheckPrime Enter any number: 23 23 is a Prime Number

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2 comment
• Heli Villarreal

Isn't it better to check up to sqrt(num) + 1 ??