Notification is a message that doesn’t appear inside the main UI of the app but as an icon in the notification area, including more details in the notification drawer.

A notification is a message you can display to the user outside of your application's normal UI.   Notifications are used to alert users on some events that requires their attention.

Notifications alert the users through various forms:

•       Display a status bar icon
•       Flash the LED
•       Vibrate
•       Ringtones

You can also show Toast notification i.e.

Toast.makeText(getApplicationContext(), "My Message", Toast.LENGTH_LONG).show();

1.      Create an Android Project
2.     Add button in activity_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity" >
 
    <Button
        android:id="@+id/btnNotif"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="Show Notification" />
 
</RelativeLayout>
 
3.      Create another layout for notification view 
 
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="horizontal" >
 
    <TextView
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text=" Your notification test is successfull !"
        android:textSize="18sp" />
 
</LinearLayout>

4.       Now add following code in MainActivity.class

package com.example.androidnotification;
 
import android.os.Bundle;
import android.app.Activity;
import android.app.Notification;
import android.app.NotificationManager;
import android.app.PendingIntent;
import android.content.Intent;
import android.support.v4.app.NotificationCompat;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
 
public class MainActivity extends Activity {
     NotificationManager notificationManager;
     static int notificationID = 100;
     
     Button btnMeaasge;
 
     @Override
     protected void onCreate(Bundle savedInstanceState) {
           super.onCreate(savedInstanceState);
           setContentView(R.layout.activity_main);
           btnMeaasge = (Button) findViewById(R.id.btnNotif);
           btnMeaasge.setOnClickListener(new OnClickListener() {
 
                @Override
                public void onClick(View v) {
                     // TODO Auto-generated method stub
                     displayMyNotification();
                }
           });
 
     }
 
     @Override
     public boolean onCreateOptionsMenu(Menu menu) {
           // Inflate the menu; this adds items to the action bar if            //it is present.
           getMenuInflater().inflate(R.menu.main, menu);
           return true;
     }
 
   // This method shows notification 
   public void displayMyNotification() {
   NotificationCompat.Builder builder = new NotificationCompat.Builder(
                     getApplicationContext());
 
           // set main title
           builder.setContentTitle("Demo Test");
 
           // set notification text
           builder.setContentText("You have received a message");
 
           // set Sticker for alert message
           builder.setTicker("New Message Alert!");
 
           // set icon
           builder.setSmallIcon(R.drawable.ic_launcher);
           // Use default sound for notification
           builder.setDefaults(Notification.DEFAULT_SOUND);
 
          notificationManager = (NotificationManager) getSystemService(getApplicationContext().NOTIFICATION_SERVICE);
           
           // A PendingIntent specifies an action to take in the
           // future
           PendingIntent myIntent = PendingIntent.getActivity(this, 0,new Intent(  this, MyNotification.class), 0);
           
           // on notification click open myIntent
           builder.setContentIntent(myIntent);
 
     /* Update the existing notification using same notification ID */
          notificationManager.notify(notificationID, builder.build());
 
     }
}

5.      Create MyNotification Activity and paste following code

package com.example.androidnotification;
 
import android.app.Activity;
import android.app.NotificationManager;
import android.os.Bundle;
import android.widget.Toast;
 
public class MyNotification extends Activity {
 
     @Override
     protected void onCreate(Bundle savedInstanceState) {
           // TODO Auto-generated method stub
           super.onCreate(savedInstanceState);
           setContentView(R.layout.notif);
                           
           // Remove notification after open this activity
        NotificationManager notificationManager = (NotificationManager)     getSystemService(getApplicationContext().NOTIFICATION_SERVICE);
           notificationManager.cancel(MainActivity.notificationID);
     }
 
}

Now run your Application

    After click on notification