How to listen volume buttons in Android background service?

This example demonstrates how do I listen volume buttons in android background service.
Step 1 − Create a new project in Android Studio, go to File ⇒ New Project and fill all required details to create a new project.
Step 2 − Add the following code to res/layout/activity_main.xml.
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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:orientation="vertical"
   android:padding="16sp"
   tools:context=".MainActivity">
<TextView
   android:layout_width="wrap_content"
   android:layout_height="wrap_content"
   android:layout_marginTop="30dp"
   android:text="Increase and decrease Volume"
   android:textSize="24sp"
   android:textStyle="bold" />
</LinearLayout>
Step 3 − Add the following code to src/MainActivity.java
import androidx.appcompat.app.AppCompatActivity;
import android.content.Context;
import android.database.ContentObserver;
import android.media.AudioManager;
import android.os.Bundle;
import android.os.Handler;
import android.widget.Toast;
import java.util.Objects;
public class MainActivity extends AppCompatActivity {
   SettingsContentObserver settingsContentObserver;
   @Override
   protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
      settingsContentObserver = new SettingsContentObserver(this, new Handler());

                  getApplicationContext().getContentResolver().registerContentObserver(android.provider.Settings.System.
      CONTENT_URI, true, settingsContentObserver);
   }
   public class SettingsContentObserver extends ContentObserver {
      int previousVolume;
      Context context;
      SettingsContentObserver(Context c, Handler handler) {
         super(handler);
         context = c;
         AudioManager audio = (AudioManager) context.getSystemService(Context.AUDIO_SERVICE);
         previousVolume =
         Objects.requireNonNull(audio).getStreamVolume(AudioManager.STREAM_MUSIC);
      }
      @Override
      public boolean deliverSelfNotifications() {
         return super.deliverSelfNotifications();
      }
      @Override
      public void onChange(boolean selfChange) {
         super.onChange(selfChange);
         AudioManager audio = (AudioManager) context.getSystemService(Context.AUDIO_SERVICE);
         int currentVolume =
         Objects.requireNonNull(audio).getStreamVolume(AudioManager.STREAM_MUSIC);
         int delta = previousVolume - currentVolume;
         if (delta > 0) {
            Toast.makeText(MainActivity.this, "Volume Decreased", Toast.LENGTH_SHORT).show();
            previousVolume = currentVolume;
         }
          else if (delta < 0) {
            Toast.makeText(MainActivity.this, "Volume Increased", Toast.LENGTH_SHORT).show();
            previousVolume = currentVolume;
         }
      }
   }
   @Override
   protected void onDestroy() {
         getApplicationContext().getContentResolver().unregisterContentObserver(settingsContentObserver);
super.onDestroy();
   }
}
Step 4 − Add the following code to androidManifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
   package="app.com.sample">
   <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>
</application>
</manifest>
Let's try to run your application. I assume you have connected your actual Android Mobile device with your computer. To run the app from the android studio, open one of your project's activity files and click the Run  icon from the toolbar. Select your mobile device as an option and then check your mobile device which will display your default screen −