Javaでsubstring()メソッドを使用して文字列を反転するにはどうすればよいですか?

package net.javaguides.corejava.string;
/**
* 
* @author Ramesh Fadatare
*
*/
public class UsingSubStringFunction {
// Function to reverse a string in Java using recursion
private static String reverse(String str) {
// base case: if string is null or empty
if (str == null || str.equals(""))
return str;
// last character + recurse for remaining string
return str.charAt(str.length() - 1) + reverse(str.substring(0, str.length() - 1));
}
public static void main(String[] args) {
String str = "javaguides";
// string is immutable
str = reverse(str);
System.out.println("Reverse of the given string is : " + str);
}
}

Reverse of the given string is : sediugavaj