Part of Continuous background operation in Android: Services

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/btnSum"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="onClickSum"
        android:text="Sum"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/btnDivide"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="onClickDivide"
        android:text="Divide"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.s0lver">

    <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:name="com.s0lver.MyBoundService" />
        <service android:name="com.s0lver.MyStartedService" />
    </application>

</manifest>

MainActivity(for bound service).java

// for bound service
package com.s0lver;

import android.content.ComponentName;
import android.content.Context;
import android.content.Intent;
import android.content.ServiceConnection;
import android.os.Bundle;
import android.os.IBinder;
import android.view.View;
import android.widget.Toast;

import androidx.appcompat.app.AppCompatActivity;

import java.util.Random;

public class MainActivity extends AppCompatActivity {
    private MyBoundService myBoundService;
    private Random random;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        random = new Random(0);
    }

    @Override
    protected void onStart() {
        super.onStart();
        Intent intent = new Intent(this, MyBoundService.class);
        bindService(intent, connection, Context.BIND_AUTO_CREATE);
    }

    @Override
    protected void onDestroy() {
        unbindService(connection);
        super.onDestroy();
    }

    private ServiceConnection connection = new ServiceConnection() {

        @Override
        public void onServiceConnected(ComponentName className,
                                       IBinder service) {
            MyBoundService.TheBinder binder = (MyBoundService.TheBinder) service;
            myBoundService = binder.getService();
        }

        @Override
        public void onServiceDisconnected(ComponentName arg0) {
        }
    };

    public void onClickSum(View view) {
        double a = random.nextDouble();
        double b = random.nextDouble();
        double sum = myBoundService.sum(a, b);
        Toast.makeText(this, String.format("%s + %s = %s", a, b, sum), Toast.LENGTH_SHORT).show();
    }

    public void onClickDivide(View view) {
        double a = random.nextDouble();
        double b = random.nextDouble();
        double division = myBoundService.divide(a, b);
        Toast.makeText(this, String.format("%s / %s = %s", a, b, division), Toast.LENGTH_SHORT).show();
    }
}

MainActivity(for started service).java

// for started service
package com.s0lver;

import android.content.Intent;
import android.os.Bundle;
import android.util.Log;

import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity {
    private Intent serviceIntent;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        serviceIntent = new Intent(this, MyStartedService.class);
        serviceIntent.putExtra("name", "Rafael");
        startService(serviceIntent);
    }

    @Override
    protected void onDestroy() {
        Log.i(this.getClass().getSimpleName(), "onDestroy()");
        stopService(serviceIntent);
        super.onDestroy();
    }
}

MyBoundService.java

package com.s0lver;

import android.app.Service;
import android.content.Intent;
import android.os.Binder;
import android.os.IBinder;
import android.util.Log;

import androidx.annotation.Nullable;

public class MyBoundService extends Service {
    public IBinder theBinder = new TheBinder();

    public class TheBinder extends Binder {
        MyBoundService getService() {
            return MyBoundService.this;
        }
    }

    @Nullable
    @Override
    public IBinder onBind(Intent intent) {
        Log.i(this.getClass().getSimpleName(), "onBind()");
        return theBinder;
    }

    public double sum(double a, double b) {
        return a + b;
    }

    public double divide(double a, double b) {
        return a / b;
    }

    @Override
    public void onDestroy() {
        Log.i(this.getClass().getSimpleName(), "onDestroy()");
        super.onDestroy();
    }
}

MyStartedService.java

package com.s0lver;

import android.app.Service;
import android.content.Intent;
import android.os.IBinder;
import android.util.Log;

import androidx.annotation.Nullable;
import androidx.core.app.NotificationCompat;

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

public class MyStartedService extends Service {
    private Timer myTimer;
    private static final int ID = new Random().nextInt(99999);

    @Nullable
    @Override
    public IBinder onBind(Intent intent) {
        return null;
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        Log.i(this.getClass().getSimpleName(), "onStartCommand()");
        String name = intent.getStringExtra("name");

        NotificationCompat.Builder b = new NotificationCompat.Builder(this, "channel_id_value");
        b.setSmallIcon(R.drawable.ic_launcher_background)
                .setContentTitle("MyStartedService")
                .setContentText("MyStartedService has been, well, started...");
        startForeground(ID, b.build());

        doTask(name);
        return START_STICKY; // START_NOT_STICKY
    }

    private void doTask(final String name) {
        myTimer = new Timer();
        myTimer.scheduleAtFixedRate(new TimerTask() {
            @Override
            public void run() {
                Log.i("MyServiceStarted", String.format("Hello %s", name));

            }
        }, 0, 3 * 1000);
    }

    @Override
    public void onCreate() {
        Log.i(this.getClass().getSimpleName(), "onCreate()");
    }


    @Override
    public void onDestroy() {
        Log.i(this.getClass().getSimpleName(), "onDestroyService()");
        myTimer.cancel();
        stopForeground(true);
        super.onDestroy();
    }
}