In this Java program, you’ll learn how to check whether a number is prime or not.

What is the Prime Number?

A prime number (or a prime) is a natural number greater than 1 that cannot be formed by multiplying two smaller natural numbers and dividing by 1 or itself. In other words, prime numbers can't be divided by other numbers than itself or 1.

For example, 7 is prime because the only ways of writing it as a product, 1 × 7 or 7 × 1, involve 7 itself.

Here is the code of the program to check the given number is prime or not:

Example 1: Java Program to Check Prime Number Using a For Loop

In this program, you will see how to check whether a number is prime or not using For Loop.

Example 1: Java Program to Check Prime Number Using a For Loop

//Java Program to Check Whether a Number is Prime or Not using For Loop
import java.util.Scanner;
public class JavaPrograms {
public static void main(String[] args) {
int num;
Scanner sc = new Scanner(System.in);
System.out.println("Enter a Number: ");
num = sc.nextInt();
boolean flag = false;
for (int i = 2; i <= num / 2; ++i) {
// condition for non-prime number
if (num % i == 0) {
flag = true;
break;
}
}
if (!flag)
System.out.println(num + " is a prime number.");
else
System.out.println(num + " is not a prime number.");
}
}

Output

Enter a Number:

7

7 is a prime number.

Example 2: Java Program to Check Prime Number Using a While Loop

In this program, you will see how to check whether a number is prime or not using While Loop.

Example 2: Java Program to Check Prime Number Using a While Loop

//Java Program to Check Whether a Number is Prime or Not using While Loop
import java.util.Scanner;
public class JavaPrograms {
public static void main(String[] args) {
int num, i = 2;
Scanner sc = new Scanner(System.in);
System.out.println("Enter a Number: ");
num = sc.nextInt();
boolean flag = false;
while (i <= num / 2) {
// condition for non-prime number
if (num % i == 0) {
flag = true;
break;
}
++i;
}
if (!flag)
System.out.println(num + " is a prime number.");
else
System.out.println(num + " is not a prime number.");
}
}

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