Check Internet Availability in Android

package com.demointernet;

import android.app.Activity;
import android.app.AlertDialog;
import android.content.Context;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.os.Bundle;
import android.widget.Toast;

public class InternetDemoActivity extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        ConnectivityManager mgr = (ConnectivityManager)getSystemService(Context.CONNECTIVITY_SERVICE);

        NetworkInfo netInfo = mgr.getActiveNetworkInfo();

        if (netInfo != null) {
        if (netInfo.isConnected())
        {
        Toast.makeText(getApplicationContext(), "Connected", 5000).show();
        // do something

        } else {
        AlertDialog.Builder alertbuilder = new AlertDialog.Builder(InternetDemoActivity.this);

        alertbuilder.setTitle("Internet");
        alertbuilder.setMessage("Internet is not available");
//        alertbuilder.setNeutralButton("Ok", );
        //alertbuilder.setIcon(R.drawable.warning);
        alertbuilder.show();
        }
        }
        else
        {
        AlertDialog.Builder alertbuilder = new AlertDialog.Builder(
        InternetDemoActivity.this);

        alertbuilder.setTitle("Internet");
        alertbuilder.setMessage("Internet is not available");
//        alertbuilder.setNeutralButton("Ok", okClickListener);

        alertbuilder.show();
        }
    }
}


Add ManifistFile two permision like

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