I have the following problem to solve:

Find the largest palindromic number made from the product of two N-digit numbers.

This is my class to find the largest palindromic number:

public class LargestPalindromeNumber { private long factorLength, highValue, max = 0, factor1 = 0, factor2 = 0; public LargestPalindromeNumber(long n){ factorLength = n; // number of digits in each factor highValue = (long) (Math.pow(10, factorLength) - 1); // highest value a factor can have } public long getLargestPalindrome1(){ for( long i = highValue; i > highValue/10 ; i = i - 1){ if(i < factor2) return max; for(long j = i ; j > highValue / 10; j = j - 1 ){ if(i % 11 == 0 || j % 11 == 0){ if(i*j < max) j = highValue/10; else{ if(isPalindrome(i * j)){ max = i * j; factor1 = i; factor2 = j; j = highValue/10; } } } }// end second for loop }// end first for loop return max; }// end getLargestPalindrome() // Checks whether a number is a palindrome public boolean isPalindrome(long n){ long reverse = 0; long value = n; while(n > 0){ reverse = (reverse * 10) + (n % 10); n = n / 10; }// end while return(value == reverse); }// end isPalindrome // Returns the value of factor1 public long getFactor1(){ return factor1; } // Returns the value of factor2 public long getFactor2(){ return factor2; } }// end LargestPalindromeNumber class

This is my main class:

import tcdIO.*; public class Main { public static void main(String[] args) { Terminal window; LargestPalindromeNumber bigPal; long ndigit; window = new Terminal("Find the Largest Palindromic Number"); window.println("This program finds the largest palindromic number that is a product of two N-Digit numbers.\n"); window.println(); ndigit = window.readInt("Enter the number of digits in the factors : "); bigPal = new LargestPalindromeNumber(ndigit); window.println(); window.println("The largest palindromic number that is a "); window.println("product of two " + ndigit + " digit numbers is: "); window.println(); window.println( "" + bigPal.getLargestPalindrome1() ); window.println(); window.println("whose factors are : " + bigPal.getFactor1() + " and " + bigPal.getFactor2() + "."); }// end main() }// end Main class

Q: Can you suggest ways to improve the efficiency of this code as it takes a long time to get an answer when i enter 9-digit by 9-digit factors, in fact I haven't waited for it to produce an answer yet.

Note:

1) The palindromic numbers I am searching for will be divisible by 11.

2) It works fine up until 8-digit by 8-digit numbers.