public class MainActivity extends AppCompatActivity implements View.OnClickListener{

    String id="channel_1";
    int importance = NotificationManager.IMPORTANCE_HIGH;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button sendNotice = (Button)findViewById(R.id.send_notice);
        sendNotice.setOnClickListener(this);
    }
    @Override
    public void onClick(View v){
        switch (v.getId()) {
            case R.id.send_notice:
                NotificationManager manager = (NotificationManager)getSystemService(NOTIFICATION_SERVICE);
                NotificationChannel mchannel = new NotificationChannel(id,"test",importance);
                manager.createNotificationChannel(mchannel);
                Notification notification;
                notification = new NotificationCompat.Builder(this,id)
                        .setContentTitle("This is content title")
                    .setContentText("This is content text")
                    .setWhen(System.currentTimeMillis())
                    .setSmallIcon(R.mipmap.ic_launcher)
                    .setLargeIcon(BitmapFactory.decodeResource(getResources(), R.mipmap.ic_launcher))
                    .build();
                manager.notify(1, notification);
                break;
            default:
                break;
        }
    }
}