Find all palindromes made from the product of two 4-digit numbers ( Java )

main.java

package com.pal;

import java.io.File;
import java.io.FileOutputStream;

public class Main {
    public static void main(String[] args) throws Exception {
        File file = new File("output.txt");
        file.createNewFile();

        FileOutputStream fileOutputStream = new FileOutputStream("output.txt");

        StringBuilder stringBuilder = new StringBuilder();

        for (int i = 1000; i <= 9999; i++) {
            if (i % 10 == 0) continue;

            for (int j = i; j <= 9999; j++) {
                if (j % 10 != 0 ) {
                    int k = i * j;

                    if (isPalindromeEx(k)) {
                        stringBuilder.append(i).append(' ').append(j).append(' ').append(k).append('\n');
                    }
                }
            }
        }

        fileOutputStream.write(stringBuilder.toString().getBytes());

        fileOutputStream.close();
    }

    public static boolean isPalindrome(int number) {
        int reversed = 0;
        int original = number, remind;

        while (number != 0) {
            remind = number % 10;
            reversed = reversed * 10 + remind;
            number /= 10;
        }

        return reversed == original;
    }

    public static boolean isPalindromeEx(int number) {
        int div = 10000000;

        if (number < 10000000) {
            div = 1000000;
        }

        int first = number / div;
        int last = number % 10;

        if (first != last) {
            return false;
        }

        return isPalindrome(number);
    }
}