Q:

Android, What is the quickest and most efficient method of converting a postcode to longitude and latitude in Java?

I know how to get a postcode from longitude and latitude coordinates but I don't know how to get the reverse (longitude and latitude from a postcode) How do I do this?
In Android
Code for getting a postcode from longitude and latitude coordinates:
Geocoder geoCoder = new Geocoder(getApplicationContext(), Locale.getDefault());
List<Address> address = null;

if (geoCoder != null){
   try {
       address= geoCoder.getFromLocation(latPoint, lngPoint, 1);
       } catch (IOException e1) {
       // TODO Auto-generated catch block
       e1.printStackTrace();
      }
      if (address.size()> 0){
        String postCode = address.get(0).getPostalCode();
      }

A:

You've pretty much answered your own question. The Android Geocoder class can be used to do both geocoding and reverse geocoding. Address-to-latlon conversion is referred to as geocoding; latlon-to-address conversion (as in your example) is referred to as reverse geocoding.  I've modified your example to show a geocoding example using a UK post code:
    Geocoder geoCoder = new Geocoder(getActivity(), Locale.getDefault());
    List<Address> address = null;

    if (geoCoder != null) {
        try {
            address = geoCoder.getFromLocationName("KT48LY", 10);
        } catch (IOException e1) {
            e1.printStackTrace();
        }
        if (address.size() > 0) {
            Address first = address.get(0);
            double lat = first.getLatitude();
            double lon = first.getLongitude();
        }
    }

