Почему не отображаются данные в recyclerview с Json?

FragmentManager fm = getSupportFragmentManager();
        Fragment fragment = fm.findFragmentById(R.id.fragment_container);
        if (fragment == null) {
            fragment =new ListFragment();
            fm.beginTransaction()
                    .add(R.id.fragment_container, fragment)
                    .commit();

package com.example.zak.mycryptofragmentlist;

import android.os.AsyncTask;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;

public class fetchData extends AsyncTask<Void,Void,Void> {
    String data ="";
    List<CurrencyModel> list=new ArrayList<>();

    @Override
    protected Void doInBackground(Void... voids) {
        try {
            URL url = new URL("https://api.coinmarketcap.com/v1/ticker/?limit=5");
            HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();
            InputStream inputStream = httpURLConnection.getInputStream();
            BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
            String line = "";
            CurrencyModelLab.getInstance();
            while(line != null){
                line = bufferedReader.readLine();
                data = data + line;
            }
            JSONArray JA = new JSONArray(data);
            for(int i=0 ;i <JA.length(); i++){
                JSONObject JO = (JSONObject) JA.get(i);


                CurrencyModelLab.getInstance().addTocurrencyModelList(new CurrencyModel(JO.getString("name"),JO.getString("price_usd"),JO.getString("price_btc")));

            }



        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (JSONException e) {
            e.printStackTrace();
        }
        return null;
    }
    @Override
    protected void onPostExecute(Void aVoid) {
        super.onPostExecute(aVoid);

          
    }
}


CurrencyModel

public class CurrencyModel {
    private String name;
    private String usdPrice;
    private String btcPrice;

    public static int count=0;


    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getUsdPrice() {
        return usdPrice;
    }

    public void setUsdPrice(String usdPrice) {
        this.usdPrice = usdPrice;
    }

    public String getBtcPrice() {
        return btcPrice;
    }

    public void setBtcPrice(String btcPrice) {
        this.btcPrice = btcPrice;
    }

    public CurrencyModel(String name, String usdPrice, String btcPrice) {
        this.name = name;
        this.usdPrice = usdPrice;
        this.btcPrice = btcPrice;

    }
}


CurrencyModelLab

public class CurrencyModelLab {
    private static CurrencyModelLab instance = null;
    private List<CurrencyModel> currencyModelList=null;

    public void setCurrencyModelList(List<CurrencyModel> currencyModelList) {
        this.currencyModelList = currencyModelList;
    }

    private CurrencyModelLab() {
        if(currencyModelList==null)
           currencyModelList=new ArrayList<>();
      /*  for (int i = 0; i <20 ; i++) {
           currencyModelList.add(new CurrencyModel(i+"coin","100"+1,"200"+2));
        }*/
    }
    public static CurrencyModelLab getInstance() {
        if (instance == null) {
            instance = new CurrencyModelLab();
        }
        return instance;
    }
    public List<CurrencyModel> getCurrencyModelList(){
        return currencyModelList;
    }

    public void addTocurrencyModelList(CurrencyModel value){

        currencyModelList.add(value);
    }
}


ListFragment

public class ListFragment  extends Fragment {
        private RecyclerView mCrimeRecyclerView;
        private CrimeAdapter mAdapter;
        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                                 Bundle savedInstanceState) {
            View view = inflater.inflate(R.layout.fragment_item_list, container, false);
            mCrimeRecyclerView = (RecyclerView) view.findViewById(R.id.recycler_view);
            mCrimeRecyclerView.setLayoutManager(new LinearLayoutManager(this.getActivity()));
            fetchData process = new fetchData();
            process.execute();
            updateUI();
            return view;
        }
        private void updateUI() {
            CurrencyModelLab currencyModellab=CurrencyModelLab.getInstance();
            List<CurrencyModel> currencyModels = currencyModellab.getCurrencyModelList();
            mAdapter = new CrimeAdapter(currencyModels);
            mCrimeRecyclerView.setAdapter(mAdapter);
        }

        private class CrimeHolder extends RecyclerView.ViewHolder implements View.OnClickListener {
            private TextView nameTextView;
            private TextView usdTextView;
            private TextView btcTextView;
            private CurrencyModel mCrime;
            public CrimeHolder(LayoutInflater inflater, ViewGroup parent) {
                super(inflater.inflate(R.layout.fragment_item, parent, false));
                itemView.setOnClickListener(this);
                nameTextView = (TextView) itemView.findViewById(R.id.nameView);
                btcTextView = (TextView) itemView.findViewById(R.id.priceBtcView);
                usdTextView = (TextView) itemView.findViewById(R.id.priceUsdView);

            }
            public void bind(CurrencyModel currencyModel) {
                mCrime = currencyModel;
                nameTextView.setText(mCrime.getName());
                usdTextView.setText(mCrime.getUsdPrice());
                btcTextView.setText(mCrime.getBtcPrice());
            }

            @Override
            public void onClick(View view) {
                Toast.makeText(getActivity(),
                        mCrime.getName() + " clicked!", Toast.LENGTH_SHORT)
                        .show();
            }
        }

        private class CrimeAdapter extends RecyclerView.Adapter<CrimeHolder> {
            private List<CurrencyModel> mCrimes;


            public CrimeAdapter(List<CurrencyModel> crimes) {
                mCrimes = crimes;
            }

            @Override
            public CrimeHolder onCreateViewHolder(ViewGroup parent, int viewType) {
                LayoutInflater layoutInflater = LayoutInflater.from(getActivity());
                return new CrimeHolder(layoutInflater, parent);
            }
            @Override
            public void onBindViewHolder(CrimeHolder holder, int position) {
                CurrencyModel currencyModel = mCrimes.get(position);
                holder.bind(currencyModel);
            }
            @Override
            public int getItemCount() {
                return mCrimes.size();
            }
        }
    }