publicrepos.java

//First we build the URI and pass it to the AsyncTask

private static final String GIT_HUB_API = "api.github.com";
private static final String USERS_ENDPOINT = "users";
private static final String REPOS_ENDPOINT = "repos";
private static final String ERROR = "error";

//(...)

Uri.Builder builder = new Uri.Builder();
builder.scheme("https")
    .authority(GIT_HUB_API)
    .appendPath(USERS_ENDPOINT)
    .appendPath(user)
    .appendPath(REPOS_ENDPOINT);
    
new NetworkWork().execute(builder.build().toString());

//(...)

//Then we build the actual AsyncTask
class NetworkWork extends AsyncTask<String, Void, String> {
  @Override
  protected String doInBackground(String... url) {
    if (url == null || url[0] == null) return ERROR;

    OkHttpClient client = new OkHttpClient();

    Request.Builder builder = new Request.Builder().url(url[0]);
    
    try (Response response = client.newCall(builder.build()).execute()) {
        if(!response.isSuccessful()) return ERROR
      
        return response.body().string();
    } catch (IOException e) {
        e.printStackTrace();
        return ERROR;
    }
  }

  @Override
  protected void onPostExecute(String s) {
    if (s.equals(ERROR)) {
        Toast.makeText(MainActivity.this, "Cannot fetch data from GitHub!", Toast.LENGTH_SHORT).show();
    } else decodeJson(s);
  }           
}

//Finally we decode the JSON
private ArrayList<String> decodeJson(String s) {
  if (TextUtils.isEmpty(s)) 
      Toast.makeText(MainActivity.this, "Empty response!", Toast.LENGTH_SHORT).show();

  ArrayList<String> repos = new ArrayList<>();
  
  try {
      JSONArray jsonRoot = new JSONArray(s);
      for (int i = 0; i < jsonRoot.length(); i++) {
          JSONObject child = jsonRoot.optJSONObject(i);
          String repoName = child.optString("name");
          if (!TextUtils.isEmpty(repoName)) repos.add(repoName);
      }

      if (!repos.isEmpty()) {
          return repos;
      } else {
          Toast.makeText(this, "Cannot extract repos from JSON!", Toast.LENGTH_SHORT).show();
      }
  } catch (JSONException e) {
      Toast.makeText(this, "Cannot decode JSON!", Toast.LENGTH_SHORT).show();
  }
}