Notification

import android.app.Notification;
import android.app.NotificationManager;
import android.app.PendingIntent;
import android.content.Intent;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;

public class MainActivity extends AppCompatActivity {
    private Button btn1;
    private Button btn2;
    private NotificationManager manager;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        btn1 = (Button) findViewById(R.id.btn1);
        btn2 = (Button) findViewById(R.id.btn2);
        btn1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                manager = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);
                Intent intent = new Intent(getApplicationContext(), Main2Activity.class);
                PendingIntent pendingIntent = PendingIntent.getActivity(
                        getApplicationContext(), 0, intent, PendingIntent.FLAG_CANCEL_CURRENT);
                Notification notification = new Notification.Builder(MainActivity.this)
                        .setContentTitle("title")
                        .setContentText("text")
                        .setSmallIcon(R.mipmap.ic_launcher)
                        .setLargeIcon(BitmapFactory.decodeResource(getResources(),R.mipmap.ic_launcher))
                        .setContentIntent(pendingIntent)
                        .setDefaults(Notification.DEFAULT_ALL)
                        .build();
                manager.notify(100,notification);
            }
        });

        btn2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                manager.cancel(100);
            }
        });
    }
}