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MainActivity[MainActivity.class]

package com.androidfeeders.serviceexample;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

/**
 * Created by ramasamy on 7/06/2018.
 * */

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

    String message = "";
    Button mstartServiceButton;
    Button mstopServiceButton;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mstartServiceButton = (Button) findViewById(R.id.start_service);
        mstopServiceButton = (Button) findViewById(R.id.stop_service);
        mstartServiceButton.setOnClickListener(this);
        mstopServiceButton.setOnClickListener(this);

    }

    @Override
    public void onClick(View view) {
        int id = view.getId();
        switch (id) {
            case R.id.start_service:
                startService(new Intent(this, MyServiceManager.class));
                break;
            case R.id.stop_service:
                stopService(new Intent(this, MyServiceManager.class));
                break;
        }
    }
}

MyServiceManager[MyServiceManager.class]

package com.androidfeeders.serviceexample;

import android.app.Notification;
import android.app.NotificationManager;
import android.app.PendingIntent;
import android.app.Service;
import android.content.Context;
import android.content.Intent;
import android.os.IBinder;
import android.support.v4.app.NotificationCompat;
import android.widget.Toast;

import java.util.Timer;
import java.util.TimerTask;

/**
 * Created by ramasamy on 7/06/2018.
 */
public class MyServiceManager extends Service {

    private final int UPDATE_INTERVAL = 1 * 1000;
    private Timer timer = new Timer();
    private static final int NOTIFICATION_EX = 1;
    private NotificationManager notificationManager;

    public MyServiceManager() {}

    @Override
    public IBinder onBind(Intent intent) {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public void onCreate() {
        // Code to execute when the service is first created
    }

    @Override
    public void onDestroy() {
        if (timer != null) {
            timer.cancel();
        }
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startid) {
        Context context = getApplicationContext();
        notificationManager = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
        int icon = android.R.drawable.stat_notify_sync;
        CharSequence tickerText = "AndroidFeeder";
        CharSequence contentTitle = "My notification";
        CharSequence contentText = "Welcome to androidfeeder";
        long when = System.currentTimeMillis();

        Intent notificationIntent = new Intent(this,MainActivity.class);
        PendingIntent contentIntent = PendingIntent.getActivity(this, 0, notificationIntent, 0);
        NotificationCompat.Builder mNotification = new NotificationCompat.Builder(context);
        mNotification.setContentTitle(contentTitle)
                .setContentText(contentText)
                .setContentIntent(contentIntent)
                .setSmallIcon(icon)
                .setContentInfo(tickerText)
                .setWhen(when);
        Notification notification = mNotification.getNotification();
        notificationManager.notify(NOTIFICATION_EX, notification);
        Toast.makeText(this, "Started!", Toast.LENGTH_LONG);
        timer.scheduleAtFixedRate(new TimerTask() {
            @Override
            public void run() {
            }
        }, 0, UPDATE_INTERVAL);
        return START_STICKY;
    }

    private void stopService() {
        if (timer != null) timer.cancel();
    }
}

Layout Resource[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:layout_gravity="center"
    android:gravity="center"
    android:layout_margin="20dp"
    tools:context=".MainActivity">

    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/start_service"
        android:text="Start Services"
        android:textColor="@android:color/white"
        android:background="@color/colorAccent"
        android:layout_centerHorizontal="true"
         />

    <Button
        android:layout_width="match_parent"
        android:textColor="@android:color/white"
        android:layout_below="@+id/start_service"
        android:layout_height="wrap_content"
        android:layout_marginTop="50dp"
        android:background="@color/colorAccent"
        android:text="Stop Services"
        android:id="@+id/stop_service"
        />

</RelativeLayout>

Gradle Scripts~build.gradle[Module:app]

apply plugin: 'com.android.application'

android {
    compileSdkVersion 28
    defaultConfig {
        applicationId "com.androidfeeders.serviceexample"
        minSdkVersion 15
        targetSdkVersion 28
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation 'com.android.support:appcompat-v7:28.0.0-alpha3'
    implementation 'com.android.support.constraint:constraint-layout:1.1.2'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'com.android.support.test:runner:1.0.2'
    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'
}

Gradle Scripts~build.gradle[Project:ServiceExample]

// Top-level build file where you can add configuration options common to all sub-projects/modules.

buildscript {
    
    repositories {
        google()
        jcenter()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:3.1.1'
        

        // NOTE: Do not place your application dependencies here; they belong
        // in the individual module build.gradle files
    }
}

allprojects {
    repositories {
        google()
        jcenter()
    }
}

task clean(type: Delete) {
    delete rootProject.buildDir
}

Resource[strings.xml]
<resources>
    <string name="app_name">ServiceExample</string>
</resources>

manifests
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.androidfeeders.serviceexample">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <service android:enabled="true" android:name=".MyServiceManager"/>

    </application>

</manifest>