Accessing a static String crashes with "Null Pointer Exception"

Question

MyService class contains static strings

package com.suprabhatam.alarm;

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

import java.text.SimpleDateFormat;
import java.util.Calendar;

public class MyService extends Service {
    private static final String TAG = "MyService";
    static public MediaPlayer mp;
    final static public String start_pause_stop_audio = "start_pause_stop_audio";
    final static public String start_audio = "start_audio";
    final static public String pause_audio = "pause_audio";
    final static public String stop_audio = "stop_audio";

    @Override
    public int onStartCommand (Intent intent, int flags, int startId) {
        Calendar cal = Calendar.getInstance();
        cal.getTime();
        SimpleDateFormat sdf = new SimpleDateFormat("HH:mm:ss");
        Log.d(TAG, sdf.format(cal.getTime()));

        if (mp == null) {
            mp = MediaPlayer.create(this, R.raw.venkateshwara_suprabhatam);
        }

        final String s_s_audio = intent.getStringExtra(MyService.start_pause_stop_audio);
        Log.d(TAG, "onStartCommand: " + s_s_audio);
        if (s_s_audio.equals(start_audio)) {
            if (!mp.isPlaying()) {
                mp.start();
            } else {
                Log.d(TAG, "already playing");
            }
        } else if (s_s_audio.equals(pause_audio)) {
            mp.pause();
        } else if (s_s_audio.equals(stop_audio)) {
            mp.seekTo(0);
            mp.pause();
        } else {
            Log.d(TAG, "UNKNOWN: " + s_s_audio);
        }

        return START_STICKY;
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
    }

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

Crashes the application, with the following message on the adb output.

ANRAppManager﹕ !!! It is not under singleton mode, U can't use it. !!!

The crash occurs only when the application is not in memory(kill ) and the MyReceiver tries to access the static strings.

It looks like the static strings are not valid until the object is created. In C++ the static strings go to the data segment and are valid when the application boots, are the rules different in java ?.

UPDATE 1: Adding the logcat message

01-20 21:53:32.849    2396-2396/com.suprabhatam.alarm D/jdwp﹕ sendBufferedRequest : len=0x45
01-20 21:53:32.854    2396-2396/com.suprabhatam.alarm W/asset﹕ AssetManager-->addDefaultAssets CIP path not exsit!
01-20 21:53:32.875    2396-2396/com.suprabhatam.alarm D/dalvikvm﹕ open_cached_dex_file : /data/app/com.suprabhatam.alarm-1.apk /data/dalvik-cache/data@app@com.suprabhatam.alarm-1.apk@classes.dex
01-20 21:53:32.897    2396-2396/com.suprabhatam.alarm D/MyService﹕ 21:53:32
01-20 21:53:32.959    2396-2396/com.suprabhatam.alarm D/MediaPlayer﹕ Don't notify duration to com.suprabhatam.alarm!
01-20 21:53:32.983    2396-2396/com.suprabhatam.alarm D/AndroidRuntime﹕ Shutting down VM
01-20 21:53:32.983    2396-2396/com.suprabhatam.alarm W/dalvikvm﹕ threadid=1: thread exiting with uncaught exception (group=0x41bea9a8)
01-20 21:53:32.984    2396-2396/com.suprabhatam.alarm W/dalvikvm﹕ threadid=1: uncaught exception occurred
01-20 21:53:32.984    2396-2396/com.suprabhatam.alarm W/System.err﹕ java.lang.RuntimeException: Unable to start service com.suprabhatam.alarm.MyService@421b4720 with null: java.lang.NullPointerException
01-20 21:53:32.984    2396-2396/com.suprabhatam.alarm W/System.err﹕ at android.app.ActivityThread.handleServiceArgs(ActivityThread.java:2867)
01-20 21:53:32.984    2396-2396/com.suprabhatam.alarm W/System.err﹕ at android.app.ActivityThread.access$1900(ActivityThread.java:165)
01-20 21:53:32.984    2396-2396/com.suprabhatam.alarm W/System.err﹕ at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1470)
01-20 21:53:32.984    2396-2396/com.suprabhatam.alarm W/System.err﹕ at android.os.Handler.dispatchMessage(Handler.java:107)
01-20 21:53:32.984    2396-2396/com.suprabhatam.alarm W/System.err﹕ at android.os.Looper.loop(Looper.java:194)
01-20 21:53:32.984    2396-2396/com.suprabhatam.alarm W/System.err﹕ at android.app.ActivityThread.main(ActivityThread.java:5391)
01-20 21:53:32.985    2396-2396/com.suprabhatam.alarm W/System.err﹕ at java.lang.reflect.Method.invokeNative(Native Method)
01-20 21:53:32.985    2396-2396/com.suprabhatam.alarm W/System.err﹕ at java.lang.reflect.Method.invoke(Method.java:525)
01-20 21:53:32.985    2396-2396/com.suprabhatam.alarm W/System.err﹕ at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:833)
01-20 21:53:32.985    2396-2396/com.suprabhatam.alarm W/System.err﹕ at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
01-20 21:53:32.985    2396-2396/com.suprabhatam.alarm W/System.err﹕ at dalvik.system.NativeStart.main(Native Method)
01-20 21:53:32.985    2396-2396/com.suprabhatam.alarm W/System.err﹕ Caused by: java.lang.NullPointerException
01-20 21:53:32.986    2396-2396/com.suprabhatam.alarm W/System.err﹕ at com.suprabhatam.alarm.MyService.onStartCommand(MyService.java:34)
01-20 21:53:32.986    2396-2396/com.suprabhatam.alarm W/System.err﹕ at android.app.ActivityThread.handleServiceArgs(ActivityThread.java:2850)
01-20 21:53:32.986    2396-2396/com.suprabhatam.alarm W/System.err﹕ ... 10 more
01-20 21:53:32.986    2396-2396/com.suprabhatam.alarm W/dalvikvm﹕ threadid=1: calling UncaughtExceptionHandler
01-20 21:53:32.987    2396-2396/com.suprabhatam.alarm E/AndroidRuntime﹕ FATAL EXCEPTION: main
    java.lang.RuntimeException: Unable to start service com.suprabhatam.alarm.MyService@421b4720 with null: java.lang.NullPointerException
            at android.app.ActivityThread.handleServiceArgs(ActivityThread.java:2867)
            at android.app.ActivityThread.access$1900(ActivityThread.java:165)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1470)
            at android.os.Handler.dispatchMessage(Handler.java:107)
            at android.os.Looper.loop(Looper.java:194)
            at android.app.ActivityThread.main(ActivityThread.java:5391)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:525)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:833)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
            at com.suprabhatam.alarm.MyService.onStartCommand(MyService.java:34)
            at android.app.ActivityThread.handleServiceArgs(ActivityThread.java:2850)
            at android.app.ActivityThread.access$1900(ActivityThread.java:165)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1470)
            at android.os.Handler.dispatchMessage(Handler.java:107)
            at android.os.Looper.loop(Looper.java:194)
            at android.app.ActivityThread.main(ActivityThread.java:5391)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:525)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:833)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
            at dalvik.system.NativeStart.main(Native Method)

UPDATE 2 second crash

01-20 21:56:23.332    2793-2799/com.suprabhatam.alarm D/jdwp﹕ handlePacket : cmd=0x1, cmdSet=0xC7, len=0x13, id=0x400000DF, flags=0x0, dataLen=0x8
01-20 21:56:42.336    2793-2805/com.suprabhatam.alarm D/ANRAppManager﹕ !!! It is not under singleton mode, U can't use it. !!!
01-20 21:57:33.091    2793-2793/com.suprabhatam.alarm I/Process﹕ Sending signal. PID: 2793 SIG: 9
01-20 21:57:38.252    3008-3008/com.suprabhatam.alarm D/MediaPlayer﹕ Don't notify duration to com.suprabhatam.alarm!
01-20 21:57:38.260    3008-3008/com.suprabhatam.alarm D/AndroidRuntime﹕ Shutting down VM
01-20 21:57:38.260    3008-3008/com.suprabhatam.alarm W/dalvikvm﹕ threadid=1: thread exiting with uncaught exception (group=0x41bea9a8)
01-20 21:57:38.260    3008-3008/com.suprabhatam.alarm W/dalvikvm﹕ threadid=1: uncaught exception occurred
01-20 21:57:38.260    3008-3008/com.suprabhatam.alarm W/System.err﹕ java.lang.RuntimeException: Unable to start service com.suprabhatam.alarm.MyService@421af568 with null: java.lang.NullPointerException
01-20 21:57:38.260    3008-3008/com.suprabhatam.alarm W/System.err﹕ at android.app.ActivityThread.handleServiceArgs(ActivityThread.java:2867)
01-20 21:57:38.260    3008-3008/com.suprabhatam.alarm W/System.err﹕ at android.app.ActivityThread.access$1900(ActivityThread.java:165)
01-20 21:57:38.260    3008-3008/com.suprabhatam.alarm W/System.err﹕ at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1470)
01-20 21:57:38.260    3008-3008/com.suprabhatam.alarm W/System.err﹕ at android.os.Handler.dispatchMessage(Handler.java:107)
01-20 21:57:38.260    3008-3008/com.suprabhatam.alarm W/System.err﹕ at android.os.Looper.loop(Looper.java:194)
01-20 21:57:38.261    3008-3008/com.suprabhatam.alarm W/System.err﹕ at android.app.ActivityThread.main(ActivityThread.java:5391)
01-20 21:57:38.261    3008-3008/com.suprabhatam.alarm W/System.err﹕ at java.lang.reflect.Method.invokeNative(Native Method)
01-20 21:57:38.261    3008-3008/com.suprabhatam.alarm W/System.err﹕ at java.lang.reflect.Method.invoke(Method.java:525)
01-20 21:57:38.261    3008-3008/com.suprabhatam.alarm W/System.err﹕ at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:833)
01-20 21:57:38.261    3008-3008/com.suprabhatam.alarm W/System.err﹕ at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
01-20 21:57:38.261    3008-3008/com.suprabhatam.alarm W/System.err﹕ at dalvik.system.NativeStart.main(Native Method)
01-20 21:57:38.261    3008-3008/com.suprabhatam.alarm W/System.err﹕ Caused by: java.lang.NullPointerException
01-20 21:57:38.261    3008-3008/com.suprabhatam.alarm W/System.err﹕ at com.suprabhatam.alarm.MyService.onStartCommand(MyService.java:34)
01-20 21:57:38.261    3008-3008/com.suprabhatam.alarm W/System.err﹕ at android.app.ActivityThread.handleServiceArgs(ActivityThread.java:2850)
01-20 21:57:38.261    3008-3008/com.suprabhatam.alarm W/System.err﹕ ... 10 more
01-20 21:57:38.261    3008-3008/com.suprabhatam.alarm W/dalvikvm﹕ threadid=1: calling UncaughtExceptionHandler
01-20 21:57:38.262    3008-3008/com.suprabhatam.alarm E/AndroidRuntime﹕ FATAL EXCEPTION: main
    java.lang.RuntimeException: Unable to start service com.suprabhatam.alarm.MyService@421af568 with null: java.lang.NullPointerException
            at android.app.ActivityThread.handleServiceArgs(ActivityThread.java:2867)
            at android.app.ActivityThread.access$1900(ActivityThread.java:165)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1470)
            at android.os.Handler.dispatchMessage(Handler.java:107)
            at android.os.Looper.loop(Looper.java:194)
            at android.app.ActivityThread.main(ActivityThread.java:5391)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:525)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:833)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
            at com.suprabhatam.alarm.MyService.onStartCommand(MyService.java:34)
            at android.app.ActivityThread.handleServiceArgs(ActivityThread.java:2850)
            at android.app.ActivityThread.access$1900(ActivityThread.java:165)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1470)
            at android.os.Handler.dispatchMessage(Handler.java:107)
            at android.os.Looper.loop(Looper.java:194)
            at android.app.ActivityThread.main(ActivityThread.java:5391)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:525)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:833)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
            at dalvik.system.NativeStart.main(Native Method)
01-20 21:57:58.221    3008-3020/com.suprabhatam.alarm D/ANRAppManager﹕ !!! It is not under singleton mode, U can't use it. !!!
01-20 22:02:38.277    3008-3008/com.suprabhatam.alarm I/Process﹕ Sending signal. PID: 3008 SIG: 9

Update 3 crash location identified

The crash is at line 32 of MyService.java

final String s_s_audio = intent.getStringExtra(MyService.start_pause_stop_audio)

01-20 22:22:42.230 6257-6257/com.suprabhatam.alarm E/MyService﹕ exception java.lang.NullPointerException at com.suprabhatam.alarm.MyService.onStartCommand(MyService.java:32) at android.app.ActivityThread.handleServiceArgs(ActivityThread.java:2850) at android.app.ActivityThread.access$1900(ActivityThread.java:165)

The problem seems to be with the intent.getStringExtra() method

The Broadcast receiver sends the following event.

Intent myIntent = new Intent(context, MyService.class);
myIntent.putExtra(MyService.start_pause_stop_audio, MyService.start_audio);
context.startService(myIntent);

How to debug this issue.

Answer 1

You should check if the intent param received in the onStartCommand() is null before doing any operation. This because the Intent can be null if the service is killed and then restarted by the system and you don't ask to resend the original intent.

Please take a deep look here and eventually change the result value for the onStartCommand() to START_REDELIVER_INTENT,

Answer 2

better solution is to get your strings from one public class for example YourConstants.java and all members inside this class to be : public static final String;

Then when you need them no matter where in your project just call YourConstants.NAME_OFF_YOUR_VARIABLE and you will not have this problem.

I always use Constants class for my public static final variables.