# Java Program to Check Prime Number

You are Here:

## What is Prime Number?

A positive integer that is divisible only by itself and 1.

Tips: It is recommended to use our online Prime Numbers calculator for better understanding.

## Examples

The following table provides few examples of prime numbers.

NumberDivisorResult
131, 13Prime Number
151, 3, 5, 15Not a Prime Number
471, 47Prime Number

## Using for loop

In the following example, we will check whether the given number (7) is a Prime number or not using for loop.

### Example

Java Compiler
public class myClass { public static void main(String[] args) { int num = 7; int i = 1; int count = 0; for(i=1; i<=num; i++) { if(num % i == 0) count++; } if(count == 2) System.out.format("%d is a prime number", num); else System.out.format("%d is not a prime number", num); } }

### Output

7 is a prime number

## Using while loop

In the following example, we will check whether the given number (7) is a Prime number or not using while loop.

### Example

Java Compiler
public class myClass { public static void main(String[] args) { int num = 7; int i = 1; int count = 0; while(num >= i) { if(num % i == 0) count++; i++; } if(count == 2) System.out.format("%d is a prime number", num); else System.out.format("%d is not a prime number", num); } }

### Output

7 is a prime number

## Using do while loop

In the following example, we will check whether the given number (7) is a Prime number or not using do while loop.

### Example

Java Compiler
public class myClass { public static void main(String[] args) { int num = 7; int i = 1; int count = 0; do { if(num % i == 0) count++; i++; }while(i <= num); if(count == 2) System.out.format("%d is a prime number", num); else System.out.format("%d is not a prime number", num); } }

### Output

7 is a prime number

## Prime Numbers between the Given Range

In the following example, we will find all the Prime numbers between 1 and 20.

### Example

Java Compiler
public class myClass { public static void main(String[] args) { int start = 1; int end = 20; int count = 0; int i = 1; System.out.println("Prime numbers between 1 and 20:"); for(start=start; start<=end; start++) { for(i=1; i<=start; i++) { if(start % i == 0) count++; } if(count == 2) System.out.print(start +" "); count = 0; } } }

### Output

Prime numbers between 1 and 20: 2 3 5 7 11 13 17 19

## Check Whether the Given Number is Prime or Composite

In the following example, we will check whether the given number is a Prime number or Composite number.

### Example

Java Compiler
import java.util.Scanner; public class myClass { public static void main(String[] args) { Scanner reader = new Scanner(System.in); System.out.print("Enter a (int) Number: "); int num = reader.nextInt(); int i; int count = 0; for(i=1; i<=num; i++) { if(num % i == 0) count++; } if(count == 2) System.out.format("%d is a prime number", num); else System.out.format("%d is a composite number", num); } }

### Output

Enter a (int) Number: 17 17 is a prime number

## Reminder

Hi Developers, we almost covered 90% of String functions and Interview Question on Java with examples for quick and easy learning.

We are working to cover every Single Concept in Java.