Volley Singleton Pattern in Android

dependencies {
    ...
    implementation 'com.android.volley:volley:1.2.1'
}

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="16dp"
    tools:context="tech.codingpoint.volleysingletonexample.MainActivity">

    <TextView
        android:id="@+id/text_view_result"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textColor="@android:color/black"
        android:textSize="20sp" />

    <Button
        android:id="@+id/button_parse"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:layout_centerHorizontal="true"
        android:layout_marginBottom="29dp"
        android:text="parse" />

</RelativeLayout>

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="tech.codingpoint.volleysingletonexample">

    <uses-permission android:name="android.permission.INTERNET" />

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

package tech.codingpoint.volleysingletonexample;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

import com.android.volley.Request;
import com.android.volley.RequestQueue;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.JsonObjectRequest;

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

public class MainActivity extends AppCompatActivity {
    private TextView mTextViewResult;
    private RequestQueue mQueue;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mTextViewResult = findViewById(R.id.text_view_result);
        Button buttonParse = findViewById(R.id.button_parse);

        mQueue = VolleySingleton.getInstance(this).getRequestQueue();

        buttonParse.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                jsonParse();
            }
        });
    }

    private void jsonParse() {

        String url = "https://api.myjson.com/bins/kp9wz";

        JsonObjectRequest request = new JsonObjectRequest(Request.Method.GET, url, null,
                new Response.Listener<JSONObject>() {
                    @Override
                    public void onResponse(JSONObject response) {
                        try {
                            JSONArray jsonArray = response.getJSONArray("employees");

                            for (int i = 0; i < jsonArray.length(); i++) {
                                JSONObject employee = jsonArray.getJSONObject(i);

                                String firstName = employee.getString("firstname");
                                int age = employee.getInt("age");
                                String mail = employee.getString("mail");

                                mTextViewResult.append(firstName + ", " + String.valueOf(age) + ", " + mail + "\n\n");
                            }
                        } catch (JSONException e) {
                            e.printStackTrace();
                        }
                    }
                }, new Response.ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError error) {
                error.printStackTrace();
            }
        });

        mQueue.add(request);
    }
}

package tech.codingpoint.volleysingletonexample;

import android.content.Context;

import com.android.volley.RequestQueue;
import com.android.volley.toolbox.Volley;

public class VolleySingleton {
    private static VolleySingleton mInstance;
    private RequestQueue mRequestQueue;

    private VolleySingleton(Context context) {
        mRequestQueue = Volley.newRequestQueue(context.getApplicationContext());
    }

    public static synchronized VolleySingleton getInstance(Context context) {
        if (mInstance == null) {
            mInstance = new VolleySingleton(context);
        }

        return mInstance;
    }

    public RequestQueue getRequestQueue() {
        return mRequestQueue;
    }
}