public static void main(String[] args) {

String s = "A man, a plan, a canal: Panama";

System.out.println(isPalindrome(s));

}

public static boolean isPalindrome(String s) {

s = s.toLowerCase();

StringBuilder l = new StringBuilder();

for (int i = 0; i < s.length(); i++) {

if ((s.charAt(i) >= '0' && s.charAt(i) <= '9') || (s.charAt(i) >= 'a' && s.charAt(i) <= 'z')) {

l.append(s.charAt(i));

}

}

int j = 0, k = l.length() - 1;

while (j < k) {

if (l.charAt(j++) != l.charAt(k--)) {

return false;

}

}

return true;

}