which of the following methods is recursive ? public static int length(String str) { if (str == null || str.equals("")) return 0: else return 1 + length(str.substring(1)); } public static int...

public static int length(String str) {

    if (str == null || str.equals(""))

       return 0:

  else

  return 1 + length(str.substring(1));

   }

public static int length(Strin str) {

    if (str == null || str.equals(""))

       return 0:

  else

  return 1;

   }

public static int length(Strin str) {

    if (str == null || str.equals(""))

  return 0:

     else

  return 1 + len(str.substring(1));

   }

public static int length(String str) {

    if (str == null || str.equals(""))

  return 0:

   }