isPrime and isPrimePalindrome example

IsPrimeAndIsPalindrome.java

package interviewProject;

import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.IntStream;

public class InterviewMain {
    public static void main(String[] args) {
        // Prime Number detector
        // Print out all number between 1 and 100
        List<Integer> primeList = IntStream.rangeClosed(1, 100)
                .boxed().collect(Collectors.toList());
        System.out.println("Opening range of numbers to check for prime:");
        System.out.println(primeList);

        ArrayList<Integer> primeNumbers = new ArrayList<>();
        Integer rangeSize = primeList.size();
        for (int i = 1; i <= rangeSize; i++) {
            if (isPrime(i)) {
                primeNumbers.add(i);
            }
        }

        System.out.println("Prime range of numbers:");
        System.out.println(primeNumbers);

        List<Integer> palindromeRange = IntStream.rangeClosed(1, 1000)
                .boxed().collect(Collectors.toList());
        Integer palindromeRangeSize = palindromeRange.size();

        ArrayList<Integer> palindromeNumbers = new ArrayList<>();
        for (int i = 1; i < palindromeRangeSize; i++) {
            if (isPrime(i)) {
                String numToString = String.valueOf(i);
                if (isPalindrome(numToString)) {
                    palindromeNumbers.add(i);
                }
            }
        }

        System.out.println("Palindrome range of numbers:");
        System.out.println(palindromeNumbers);
    }

    public static boolean isPrime(Integer n) {
        // def: only div by 1 and itself
        // edge cases
        if (n <= 1) {
            return false;
        }
        if (n <= 3) {
            return true;
        }

        // we can skip the middle five numbers
        if (n % 2 == 0 || n % 3 == 0) {
            return false;
        }

        // check from 2 to n-1
        for (int i = 5; i * i <= n; i = i + 6) {
            if (n % i == 0 || n % (i + 2) == 0) {
                return false;
            }
        }

        return true;
    }

    // check if the provided number is a palindrome
    public static boolean isPalindrome(String str) {
        int strLength = str.length();
        // StringBuilder vs. String concatenation:
        // https://stackoverflow.com/questions/1532461/stringbuilder-vs-string-concatenation-in-tostring-in-java
        StringBuilder reverseStrBuilder = new StringBuilder();

        for (int i = (strLength - 1); i >= 0; --i) {
            reverseStrBuilder.append(str.charAt(i));
        }

        return str.equalsIgnoreCase(reverseStrBuilder.toString());
    }
}