reverse a string using recursion with java

I am trying to write a recursion to reverse a String.This is my approach.

    public static void main(String[] args) {
        String str = "abc";
        String b = reverseString(str);
        System.out.println(b);
    }

    public static String reverseString(String a){
        if (a.isEmpty()){
            return a;
        }

        return reverseString(a.substring(1)) + a.charAt(0);
    }

I dont get why when it reaches the base case, where my a is already empty but I am still able to print out the reversed string.

Answer

you are not implementing any recursion, you just replaced two halves of a string.

public static void main(String[] args) {
    String str = "abcd";

    String b = reverseString(str);
    System.out.println(b);
}

public static String reverseString(String str) {
    int p = str.length() / 2;
    if (str.length() == 1)
        return str;
    String prefix = reverseString(str.substring(p, str.length()));
    String suffix = reverseString(str.substring(0, p));

    return prefix + suffix;
}