Creating a recursive method for Palindrome

Question

I am trying to create a Palindrome program using recursion within Java but I am stuck, this is what I have so far:

 public static void main (String[] args){
         


        

Answer 1

Here are three simple implementations, first the oneliner:

public static boolean oneLinerPalin(String str){
    return str.equals(new StringBuffer(str).reverse().toString());
}

This is ofcourse quite slow since it creates a stringbuffer and reverses it, and the whole string is always checked nomatter if it is a palindrome or not, so here is an implementation that only checks the required amount of chars and does it in place, so no extra stringBuffers:

public static boolean isPalindrome(String str){

    if(str.isEmpty()) return true;

    int last = str.length() - 1;        

    for(int i = 0; i <= last / 2;i++)
        if(str.charAt(i) != str.charAt(last - i))
            return false;

    return true;
}

And recursively:

public static boolean recursivePalin(String str){
    return check(str, 0, str.length() - 1);
}

private static boolean check (String str,int start,int stop){
    return stop - start < 2 ||
           str.charAt(start) == str.charAt(stop) &&
           check(str, start + 1, stop - 1);
}