Java Program to Perform Fermat Primality Test

This is a Java Program to Implement Fermat Primality Test Algorithm. Fermat Primality Test is an algorithm which is used to determine if a given number is prime or not.

Here is the source code of the Java Program to Implement Fermat Primality Test Algorithm. The Java program is successfully compiled and run on a Windows system. The program output is also shown below.

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/**
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 ** Java Program to Implement Fermat Primality Test Algorithm

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 **/
```
```
 
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```
import java.util.Scanner;
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import java.util.Random;
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```
 
```
```
/** Class FermatPrimality **/
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public class FermatPrimality
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{
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    /** Function to check if prime or not **/

    public boolean isPrime(long n, int iteration)

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    {
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        /** base case **/
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        if (n == 0 || n == 1)
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            return false;
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        /** base case - 2 is prime **/
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        if (n == 2)
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            return true;
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        /** an even number other than 2 is composite **/

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        if (n % 2 == 0)
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            return false;
```
```
 
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        Random rand = new Random();
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        for (int i = 0; i < iteration; i++)

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        {
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            long r = Math.abs(rand.nextLong());

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            long a = r % (n - 1) + 1;
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            if (modPow(a, n - 1, n) != 1)

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                return false;
```
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        }
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        return true;        
```
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    }
```

    /** Function to calculate (a ^ b) % c **/

    public long modPow(long a, long b, long c)

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    {
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        long res = 1;
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        for (int i = 0; i < b; i++)
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        {
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            res *= a;
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            res %= c; 
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        }
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        return res % c;
```
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    }    
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    /** Main function **/
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    public static void main (String[] args)

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    {
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        Scanner scan = new Scanner(System.in);

        System.out.println("Fermat Primality Algorithm Test\n");

        /** Make an object of FermatPrimality class **/

        FermatPrimality fp = new FermatPrimality();

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        /** Accept number **/
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        System.out.println("Enter number\n");

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        long num = scan.nextLong();
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        /** Accept number of iterations **/

        System.out.println("\nEnter number of iterations");

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        int k = scan.nextInt();
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        /** check if prime **/
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        boolean prime = fp.isPrime(num, k);

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        if (prime)
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            System.out.println("\n"+ num +" is prime");

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        else
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            System.out.println("\n"+ num +" is composite");

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    }
```
```
}
```

Fermat Primality Algorithm Test
 
Enter number
 
999983
 
Enter number of iterations
2
 
999983 is prime

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