Java How To - Palindrome Check

How To Check if a String Is a Palindrome

Learn how to check whether a word reads the same forward and backward (like "level"):

String text = "level";
boolean isPalindrome = true;

for (int i = 0; i < text.length() / 2; i++) {
  if (text.charAt(i) != text.charAt(text.length() - 1 - i)) {
    isPalindrome = false;
    break;
  }
}

if (isPalindrome) {
  System.out.println(text + " is a palindrome");
} else {
  System.out.println(text + " is not a palindrome");
}

Explanation: We compare the first character with the last, the second with the second-last, and so on.
- If all pairs match, the string is a palindrome.
- If any pair does not match, it is not a palindrome.
For example, in "level":

• l == l
• e == e

Using StringBuilder

You can also use StringBuilder, which is a special Java class that makes it easy to work with and change strings (for example, reversing them):

String text = "level";
String reversed = new StringBuilder(text).reverse().toString();

if (text.equalsIgnoreCase(reversed)) {
  System.out.println(text + " is a palindrome");
} else {
  System.out.println(text + " is not a palindrome");
}

Explanation: We take the string text and use StringBuilder.reverse() to create its reverse. If the original and reversed strings are the same (ignoring case with equalsIgnoreCase()), then it is a palindrome.