How to find array index value in android

I'm looking for a way to find the index position of arrays and i want to store that value in String but how can we do this please help me some one

my arrayLists:-

  String[] planets = new String[] { "Mercury","Mercury", "Venus", "Earth", "Mars",
            "Jupiter", "Saturn", "Uranus", "Neptune"};

 String[] Ruppes = new String[] { "100", "200","1000", "300", "400",
            "500", "600", "700", "800"};