A prime number is a natural number greater than 1, that’s not divisible by any other number. In simple terms a prime number has only two positive divisors 1 and itself for example 2,3,5,7—– are prime numbers. Natural numbers other than prime numbers are known as composite numbers.

## Java Code for Prime Number

Lets see the Java code for prime number. There are many different ways to write code to check whether a given number is a prime number or not. The simplest approach for checking prime numbers is to use a loop to iterate through all the numbers from 2 to the square root of the number. If any of those numbers divide the given number into two equal parts then the given number is not a prime number. Otherwise, it is a prime number.

```
package gangforcode;
import java.util.Scanner;
public class Prime {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
System.out.println("Enter the number");
int n = sc.nextInt();
if(n<2){
System.out.println("Not Prime");
}
else{
boolean isPrime = true;
for(int i=2;i<=Math.sqrt(n);i++){
if(n%i==0){
isPrime=false;
break;
}
}
if(isPrime)
System.out.println("Prime Number");
else System.out.println("Not Prime");
}
}
}
```

## Output

Even though this is the simplest approach for checking prime numbers but, it can be slow for large numbers. The more efficient approach to check prime numbers is the **Sieve of Eratosthenes**. Sieve of Eratosthenes is a simple algorithm for finding all the prime numbers in the given range.