Java Program to Print alternate Prime numbers

In this tutorial, we will write a Java program to display alternate prime numbers upto a given value.

Java Example to print alternate prime numbers

In the following example we have two user defined methods: checkPrime() and printAltPrime().

The checkPrime() method checks whether the number passed as an argument is prime or not, if the number is prime, this method returns 1 else it returns false.

The printAltPrime() method prints the alternate prime numbers upto the value passed as an argument.

Do read the comments to understand the logic of the program.

class JavaExample  
{ 

    //method for checking prime number
    static int checkPrime(int num) 
    { 
	int i, flag = 0; 
	for(i = 2; i<= num / 2; i++) 
	{ 
	   if(num % i == 0) 
	   { 
	       flag = 1; 
	       break; 
	   } 
	} 

	/* If flag value is 0 then the given number num
	 * is a prime number else it is not a prime number
	 */
	if(flag == 0) 
	   return 1; 
	else
	   return 0; 
    } 

    //Method for printing alternate prime numbers
    static void printAltPrime(int n) 
    { 
	/* When the temp value is odd then we are
	 * not printing the prime number and when it is
	 * even then we are printing it, this way we are
	 * displaying alternate prime numbers
	 */
	int temp = 2; 

	for(int num = 2; num <= n-1; num++) 
	{ 
	   //checking each number whether it is prime or not
	   if (checkPrime(num) == 1) 
	   {  
		// if temp is even then only print the prime number
		if (temp % 2 == 0) 
		   System.out.print(num + " "); 

		temp ++; 
	   } 
	} 
    } 

    public static void main(String[] args)  
    { 
	int num = 20; 
	System.out.print("Alternate prime numbers upto " + num+" are: ");  
	printAltPrime(num); 
    } 
}

Output:

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