private class GetSamplingPoints extends AsyncTask<ArrayList<Float>, Void, JSONArray> {
    @Override
    protected JSONArray doInBackground(ArrayList<Float>... params) {

        // params comes from the execute() call: params[0] is the url.
        try {

            Uri.Builder builder = new Uri.Builder();
            builder.scheme("http")
                    .authority("environment.data.gov.uk")
                    .appendPath("water-quality")
                    .appendPath("id")
                    .appendPath("sampling-point")
                    .appendQueryParameter("lat", params[0].)
                    .appendQueryParameter("long", params[1])
                    .appendQueryParameter("dist", "10")
                    .appendQueryParameter("samplingPointStatus", "open");
            String myUrl = builder.build().toString();

            URL url = new URL(myUrl);
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setReadTimeout(10000 /* milliseconds */);
            conn.setConnectTimeout(15000 /* milliseconds */);
            conn.setRequestMethod("GET");
            // Not sure if true or false
            conn.setDoInput(false);
            // Starts the query
            conn.connect();
            int response = conn.getResponseCode();
            Log.d(DEBUG_TAG, "The response is: " + response);
            is = conn.getInputStream();

            // Convert the InputStream into a string
            JSONArray SamplingPoints = readIt(is, len);
            return contentAsString;
        } catch (IOException e) {
            return "Unable to retrieve web page. URL may be invalid.";
        }
    }
    // onPostExecute displays the results of the AsyncTask.
    @Override
    protected void onPostExecute(String result) {
        textView.setText(result);
    }
}
    // Given a URL, establishes an HttpUrlConnection and retrieves
// the web page content as a InputStream, which it returns as
// a string.
    private String downloadUrl(String myurl) throws IOException {
        InputStream is = null;
        // Only display the first 500 characters of the retrieved
        // web page content.
        int len = 500;

        try {
            URL url = new URL(myurl);
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setReadTimeout(10000 /* milliseconds */);
            conn.setConnectTimeout(15000 /* milliseconds */);
            conn.setRequestMethod("GET");
            conn.setDoInput(true);
            // Starts the query
            conn.connect();
            int response = conn.getResponseCode();
            Log.d(DEBUG_TAG, "The response is: " + response);
            is = conn.getInputStream();

            // Convert the InputStream into a string
            String contentAsString = readIt(is, len);
            return contentAsString;

            // Makes sure that the InputStream is closed after the app is
            // finished using it.
        } finally {
            if (is != null) {
                is.close();
            }
        }
    }
        }
@@ -11,11 +11,8 @@
 ass 
-Get
 Samp
@@ -21,16 +21,19 @@
 ngPoints
+API
  extends
@@ -53,21 +53,22 @@
 rayList%3C
-Float
+String
 %3E, Void,
@@ -148,13 +148,14 @@
 ist%3C
-Float
+String
 %3E...
@@ -594,12 +594,15 @@
 rams
-%5B0%5D.
+.get(0)
 )%0A  
@@ -659,11 +659,15 @@
 rams
-%5B1%5D
+.get(1)
 )%0A  
@@ -3111,20 +3111,21 @@
    %7D%0A    %7D%0A        %7D
+%0A

Change class param to ArrayList<String>