Palindrome discoverer

The problem

Write program in java that accepts users input and validates if the input is a palindrome. A palindrome is a word that reads the same forwards as it does backwards. For this exercise we will consider a palindrome a palindrome without punctuation.

Breaking it down

Ask user for word or phrase

// Create a Scanner object for keyboard input.
Scanner keyboard = new Scanner(;

// Get user input 
System.out.print("Enter a word or phrase: ");
String userInput = keyboard.nextLine();

Write a method isPalindrome

 * Method should return true if a string is identified as a palindrome. 
 * There are many ways to do a palindrome check, this is just one of them.
 * If you are performing checks on very, very long strings you may want to 
 * consider another algorithm.
 * @param str
 * @return
public static boolean isPalindrome(String str) {

    if (str.length() <= 1) {
        return true;
    } else {
        String toCompare = str.replaceAll("\\s+","");
        StringBuffer buffer = new StringBuffer(toCompare);
        String reversedString = buffer.reverse().toString();
        if (reversedString.equalsIgnoreCase(toCompare)) {
            return true;
        } else {
            return false;

Check word or phrase, display result

boolean isAPalindrome = isPalindrome(userInput);

if (isAPalindrome) {
    System.out.print("The word or phrase is a palindrome");   
} else {
    System.out.print("Sorry the word or phrase is NOT a palindrome");


Enter a word or phrase: Able was I ere I saw Elba
The word or phrase is a palindrome

Unit tests

public void is_a_palindrome_single_char () {

public void is_a_palindrome () {

public void is_a_palindrome_mixed_case () {
    assertTrue(PalindromeDiscoverer.isPalindrome("A but tuba"));

public void is_a_palindrome_longer_phrase () {
    assertTrue(PalindromeDiscoverer.isPalindrome("Able was I ere I saw Elba"));

public void is_not_a_palindrome () {
    assertFalse(PalindromeDiscoverer.isPalindrome("Free beer, I am there..."));

Level Up

  • Validate user input
  • Allow user to enter in more than one check
  • A palindrome is often considered true excluding spaces or punctuation, enhance the program to punctuation