Palindromic Prime - Combining isPrime and isPalindrome

[javanewbie123]

Hi guys I am somewhat new to Java programming and am looking for some help. I have 2 programs, isPrime and isPalindrome, and I would like to combine them so that the new program displays the first 100 prime numbers that are palindromes. I am having a hard time doing this and was wondering if anyone could help me. Thanks

isPrime Code:

public class ShowPrimes 
{
	static final int TOTAL_PRIMES_TO_FIND = 100;	// number of primes to be found in this application
	static final int PRIMES_SHOWN_PER_LINE = 10;	// number of primes shown per display line	
	
	public static void main(String[] args) 
	{
		int lastPrimeFound;				// last prime number found via test
		int count;						// count of number of primes found
		
		System.out.println("Here are the first 100 prime numbers:  ");
		System.out.printf("%5d%5d", 2,3);	// clearly  2 and 3 are  prime numbers!
		lastPrimeFound = 3;						// our first number to test
		
		for (count = 2; count < TOTAL_PRIMES_TO_FIND; )
		{
			++count;											// count of the prime we are presently finding
			lastPrimeFound = getNextPrime(lastPrimeFound);		// candidate for next prime from previous prime
			System.out.printf("%5d", lastPrimeFound);			// prime found, so display it
			if (count % PRIMES_SHOWN_PER_LINE == 0)
				System.out.printf("\n");	
		}
	}

	// returns the next prime number using value of primeJustFound to generate a next candidate
	
	private static int getNextPrime(int primeJustFound)
	{
		int candidate;		// candidate value tested for a prime
		
		candidate = primeJustFound + 2;
		while (!isPrime(candidate))
		{
			candidate += 2;
		}
		
		return candidate;
	}
	// returns true if testValue is prime and false if testValue is divisible by some number other than 1 or itself
		
	private static boolean isPrime(int possiblePrime)
	{
		boolean factorFound = false;				// set to true if loop finds a factor
		double limit = Math.sqrt(possiblePrime);	// upper limit on integers to test	
		int possibleFactor;							// int value that could be a factor of possiblePrime
		
		possibleFactor = 3;								// even numbers are not part of the logic
		while (possibleFactor <= limit && !factorFound)	// exits with factor found or no more factors to test
		{
			if (possiblePrime % possibleFactor == 0)	// factor found; no longer prime
				factorFound = true;
			else
				possibleFactor+= 2;
		}
		
		return !factorFound;
	}	
}

isPalindrome Code:

import java.util.*;

// Main is a driver for the method isPalindrome

public class TestIsPalindrome 
{
	static Scanner keyboard = new Scanner(System.in);
	
	public static void main(String[] args)
	{
		int testValue;
		
		System.out.print("Enter a test value:  ");
		testValue = keyboard.nextInt( );
		keyboard.nextLine( );

		if (isPalindrome(testValue))
			System.out.println("The number " + testValue + " is a palindrome.");
		else
			System.out.println("The number " + testValue + " is not a palindrome.");				
	}

	// returns true if testValue is a palindrome; otherwise returns false
	
	private static boolean isPalindrome(int testValue)
	{
		int reversedNumber;				// least significant digit of testValue is most significant and vice-versa 
		int generatorForReversedNumber;	// gotten by "extracting" and weighting each digit from testValue
		int nextDigit;					// to be extracted from testValue
		
		reversedNumber = 0;				// sum accumulator.. initially no digits accumulated
		generatorForReversedNumber = testValue;
		while (generatorForReversedNumber > 0)
		{
			nextDigit = generatorForReversedNumber % 10;
			reversedNumber = 10 * reversedNumber + nextDigit;
			generatorForReversedNumber /= 10;
		}
		
		return testValue == reversedNumber;
	}
}

how would I go about combining them? I tried changing up the main but still doesn't work.

[Norm]

Could you call one method and if it returns true, then call the other?

[javanewbie123]

not sure how to do that. could you demonstrate?

[ozzyman]

Method to check if a number is a palindrome

public boolean isPalindrome(int number) {
   //code to find out if it is a palindrome
   ... //if it is a palindrome, return true;
   //otherwise:
   return false;
}

The part of your code where you are checking for both palindrome and prime

List<Integer> listOfPrimes = getANumberOfPrimes(100);
for (int prime:listOfPrimes) {
    if (isPalindrome(prime)) {
        //it is both a palindrome and a prime
        ...
    }
}

Method to get a number of primes

public List<Integer> getANumberOfPrimes(int number) {
    ...
}

[Norm]

while count < 100
get next prime
is it a palindrome?
save it and incr the count
end loop