Project Euler Problem #4 - Largest Palindrome Product (in Java)

```import java.lang.StringBuilder;

public class Problem_4_Largest_Palindrome_Product {

/* A palindromic number reads the same both ways. The largest palindrome made from the product of two 2-digit numbers is 9009 = 91 * 99.
Find the largest palindrome made from the product of two 3-digit numbers. */
public static void main(String[] args) {
System.out.println(findLargestPalindrome());
}

/* determines whether or not an integer is a palindrome;
that is, if it reads the same from both ways */
public static boolean isPalindrome(long n) {
String s = String.valueOf(n);
StringBuilder reverseString = new StringBuilder();

// reverse the string
for (int i = s.length() - 1; i > -1; i--) {
reverseString.append(s.charAt(i));
}

return reverseString.toString().equals(s);
}

/* using the reverse() method in the StringBuilder class
instead of reversing the string through iterations */
public static boolean isPalindrome2(long n) {
String s = String.valueOf(n);
return new StringBuilder(s).reverse().toString().equals(s);
}

/* returns largest palindrome that is a multiple of two 3 digit numbers
and returns -1 if no such palindrome exists */
public static long findLargestPalindrome() {
long palindrome = -1;

for (int i = 999; i > 99; i--) {
for (int j = i; j > 99; j--) {

// if product is palindrome and is greater than last recorded palindrome
if (isPalindrome(i * j) && i * j > palindrome) {
palindrome = i * j;
}
}
}
return palindrome;
}
}```

Created: February 19, 2014
Last Updated: August 27, 2014
Completed in full by: Michael Yaworski