Monitor battery level

package com.example.androidbattery;

import android.os.Bundle;
import android.app.Activity;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.widget.TextView;

public class MainActivity extends Activity {
 
 TextView batteryStatus;

 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);
  batteryStatus = (TextView)findViewById(R.id.batterystatus);
  
  IntentFilter batteryFilter = new IntentFilter(Intent.ACTION_BATTERY_CHANGED);
  registerReceiver(batteryMonitor, batteryFilter);
 }

 private BroadcastReceiver batteryMonitor
 = new BroadcastReceiver(){

  @Override
  public void onReceive(Context arg0, Intent arg1) {
   int batteryLevel = arg1.getIntExtra("level", 0);
   batteryStatus.setText("Battery level = " + String.valueOf(batteryLevel) + "%");
  }};

}

<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"
    tools:context=".MainActivity" 
    android:orientation="vertical">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/hello_world" />
    <TextView
        android:id="@+id/batterystatus"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>
        
</LinearLayout>