How to Detect Network Connectivity on Android

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.TextView;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
 
// (4) Setting up an interface for the MainActivity
interface MainActivityDataTaskNotification {
    void notifyMainActivity(String connStatus, String connInstruction);
}
 
 
public class MainActivity extends AppCompatActivity {
 
    // Activity declaration of textviews
    TextView connectivityStatus;
    TextView connectivityInstruction;
 
    @Override  // (1) MainActivity's  onCreate method
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
 
        // Assignment of the Textviews from the user interface. (See activity_main.xml)
        connectivityStatus =  findViewById(R.id.connectionStatus);
        connectivityInstruction =  findViewById(R.id.requestContainerInstruction);
    }
 
 
    /**
     * (2) Request Data Callback method of the @+id/requestData button in activity_main.xml
     *
     * @param view : the view from the activity, in this case the button.
     *
     */
    public void requestDataCallback(View view) {
 
        try {
            String connectionInstruction = "";
            String connectionStatus = "";
            if (isNetworkReachable()) {
                DataTask dataTask = new DataTask(mainActivityDataTaskNotification);
 
                connectionInstruction = dataTask.execute("https://httpbin.org/get?arg1=1&arg2=2").get();
                connectionStatus = "Connection Status: Online";
            } else {
                connectionInstruction = "Please check your internet connection and try your request again.";
                connectionStatus = "Connection Status: Offline";
            }
 
            mainActivityDataTaskNotification.notifyMainActivity(connectionStatus, connectionInstruction);
        } catch (Exception e) {
            String connectionInstruction = e.getMessage();
            String connectionStatus = "";
            mainActivityDataTaskNotification.notifyMainActivity(connectionStatus, connectionInstruction);
        }
    }
 
    /**
     *  (3) Calling into the ConnectivityManagerr : Class that answers queries about the state of network connectivity.
     * It also notifies applications when network connectivity changes.
     * @url  https://developer.android.com/reference/android/net/ConnectivityManager
     *
     */
    private boolean isNetworkReachable() {
        ConnectivityManager manager =
                (ConnectivityManager) getSystemService(this.CONNECTIVITY_SERVICE);
        NetworkInfo networkInfo = manager.getActiveNetworkInfo();
        if (networkInfo != null && networkInfo.isConnected()) {
            return true;
        }
        return false;
    }
 
    /**
     * (4) MainActivityDataTaskNotification (Closure) : Interface Method.
     * 
     */
    MainActivityDataTaskNotification mainActivityDataTaskNotification = new MainActivityDataTaskNotification() {
        @Override
        public void notifyMainActivity(String connStatus, String connInstruction) {
            connectivityInstruction.setText(connInstruction);
            connectivityStatus.setText(connStatus);
        }
    };
 
}

package com.agnosticdev.networkconnectivity;
 
import android.os.AsyncTask;
import android.util.Log;
 
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
 
 
public class DataTask extends AsyncTask<String, Void, String> {
 
    private MainActivityDataTaskNotification mainActivityInterface;
 
    public DataTask(MainActivityDataTaskNotification mainActivityInterface) {
        this.mainActivityInterface = mainActivityInterface;
    }
 
    @Override
    /**
     * (2) doInBackground
     * Notifies the main thread and calls the MainActivity method after onPreExecute is called.
     * <String, _, _> in the AsyncTask declaration.
     * @param String urlParams : passed into the execute() method.
     *
     */
    public String doInBackground(String... urlParams) {
 
 
        String connectionInstruction = "";
        String stringBufferData = "";
        URL passedInURL;
        HttpURLConnection connection = null;
        try {
 
            if (urlParams.length > 0) {
                passedInURL = new URL(urlParams[0]);
                connection = (HttpURLConnection) passedInURL.openConnection();
                InputStream fd = connection.getInputStream();
                InputStreamReader fdRead = new InputStreamReader(fd);
                int buffer = fdRead.read();
                while (buffer != -1) {
                    char bufferedCharacter = (char) buffer;
                    stringBufferData += bufferedCharacter;
                    buffer = fdRead.read();
                }
            }
 
            /// Do something meaningful with the stringBufferData here.
            /// For example, parse it into a model object.
 
            /// Meanwhile, onPostExecute to so this value can be passed back to the UI thread.
            connectionInstruction = "Based upon your last network request, your connectivity is good.";
 
 
        } catch (Exception e) {
            connectionInstruction = e.toString();
            e.printStackTrace();
        }
 
        return connectionInstruction;
    }
 
    @Override
    /**
     * (1) onPreExecute
     * Notifies the main thread and calls the MainActivity method before doInBackground is called.
     * <_, Void, _> in the AsyncTask declaration.
     *
     */
    public void onPreExecute() {
        this.mainActivityInterface.notifyMainActivity("Connection Status: Checking",
                "Waiting for connection to finish");
    }
 
    @Override
    /**
     * (3) onPostExecute
     * Returns the result from doInBackground and notifies the MainActivity on the main thread.
     * <_, _, String> in the AsyncTask declaration.
     *
     * @param String response : returned from the doInBackground method.
     */
    public void onPostExecute(String response) {
        String status = "Online";
        // Not a long term solution, but one technique could be to check for (UnknownHostException).
        if (response.contains("UnknownHostException")) {
            status = "Offline";
        }
        this.mainActivityInterface.notifyMainActivity("Connection Status: " + status,
                response);
    }
 
}