Another common Java exercise is to verify if a String is a Palindrome

The algorithm is:

• Split the String into an array with all the characters
• Reverse the array
• Join the array again
• Check if the reversed string is equal to the input

Reversing the array

public class StringReverser {
    public static String reverse(String s1){
        if(isNull(s1)){
            return null;
        }
        List<String> charList = asList(s1.split(""));
        Collections.reverse(charList);
        return String.join("", charList);
    }
}

Palindrome class

public class Palindrome {

    public static boolean isPalindrome(String s1){
        if(isNull(s1)){
            return false;
        }
        String reversed = StringReverser.reverse(s1);
        return reversed.equals(s1);
    }
}

Source code: Palindrome