Android App crashes on startup while reading objects from java.lang.NullPointerException

Question

I am working on my first Android app. It was working fine until I decided to add a functionality to save and load objects and settings on OnCreate and onRestart. After that the app crashes on startup. Here is the setSettings that I call from OnCreate.

public void setSettings(){
    SharedPreferences settings = getSharedPreferences("Prefs",0);
    newGame = settings.getBoolean("newGame", true);
    autoDecide = settings.getBoolean("autoDecide", true);
    saved = settings.getBoolean("saved", false);
    if (saved){     
        player1 = readPlayer("Player 1");
        player2 = readPlayer("Player 2");
        ((TextView)findViewById(R.id.Player1name)).setText(""+player1.name);
        ((TextView)findViewById(R.id.Player2name)).setText(""+player2.name);
        ((TextView)findViewById(R.id.player1wins)).setText(""+player1.totalWins);
        ((TextView)findViewById(R.id.player2wins)).setText(""+player2.totalWins);
        ((TextView)findViewById(R.id.Player1life)).setText(""+player1.life);
        ((TextView)findViewById(R.id.Player2life)).setText(""+player2.life);
    }
}

the saved boolean is supposed to be false until I saved things, but I don't think it is working. Here is the readPlayer that it calls where the problem might be.

    public Player readPlayer(String loc)  {
    //FileInputStream fis;
        try {
        BufferedInputStream buf = new BufferedInputStream( openFileInput(loc));
        ObjectInputStream stream = new ObjectInputStream(buf);
        Player re = (Player) stream.readObject();
        stream.close();
        buf.close();
        return re;
        } catch (FileNotFoundException e) {
        //e.printStackTrace();
            return new Player(loc);
        } catch (IOException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    return new Player(loc);
}

and here is the logCat that I get when it crashes.

05-26 03:49:05.739: E/AndroidRuntime(391): java.lang.RuntimeException: Unable to start activity    ComponentInfo{jjcard.app.lifecount/jjcard.app.lifecount.Life_counterActivity}: java.lang.NullPointerException
05-26 03:49:05.739: E/AndroidRuntime(391):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1815)
05-26 03:49:05.739: E/AndroidRuntime(391):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1831)
05-26 03:49:05.739: E/AndroidRuntime(391):  at android.app.ActivityThread.access$500(ActivityThread.java:122)
05-26 03:49:05.739: E/AndroidRuntime(391):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1024)
05-26 03:49:05.739: E/AndroidRuntime(391):  at android.os.Handler.dispatchMessage(Handler.java:99)
05-26 03:49:05.739: E/AndroidRuntime(391):  at android.os.Looper.loop(Looper.java:132)
05-26 03:49:05.739: E/AndroidRuntime(391):  at android.app.ActivityThread.main(ActivityThread.java:4123)
05-26 03:49:05.739: E/AndroidRuntime(391):  at java.lang.reflect.Method.invokeNative(Native Method)
05-26 03:49:05.739: E/AndroidRuntime(391):  at java.lang.reflect.Method.invoke(Method.java:491)
05-26 03:49:05.739: E/AndroidRuntime(391):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:841)
05-26 03:49:05.739: E/AndroidRuntime(391):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:599)
05-26 03:49:05.739: E/AndroidRuntime(391):  at dalvik.system.NativeStart.main(Native Method)
05-26 03:49:05.739: E/AndroidRuntime(391): Caused by: java.lang.NullPointerException
05-26 03:49:05.739: E/AndroidRuntime(391):  at jjcard.app.lifecount.Life_counterActivity.setSettings(Life_counterActivity.java:72)
05-26 03:49:05.739: E/AndroidRuntime(391):  at jjcard.app.lifecount.Life_counterActivity.onCreate(Life_counterActivity.java:42)
05-26 03:49:05.739: E/AndroidRuntime(391):  at android.app.Activity.performCreate(Activity.java:4397)
05-26 03:49:05.739: E/AndroidRuntime(391):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1048)
05-26 03:49:05.739: E/AndroidRuntime(391):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1779)

I don't know if you would need the player creation but here it is

    public Player(String nameN){
    name = nameN;
    life = 8000;
    totalWins = 0;
    totalLosses = 0;
    wins = new HashMap<String, Integer>();
}

It happens everytime I start it up and I've tried a few things as you can probably see by the code with no success. I tried searching around but I can't find anything. Hope you guys can help.
EDIT: here is line 72 that the LogCat shows is the problem.

((TextView)findViewById(R.id.Player1name)).setText(""+player1.name);

So it looks like you are right, it might be making reading an empty object instead of returning a new player like I thought it would. And since I don't know a lot about making writing and reading objects, I just used defaultWriteObject and defaultReadObject

    private void writeObject(ObjectOutputStream out) throws IOException{
    out.defaultWriteObject();
}
private void readObject(ObjectInputStream in) throws ClassNotFoundException, IOException{
    in.defaultReadObject();
}

EDIT: after changing the read/write and trying to check for the name being null, it still doesn't work. I even tried setting the text to a String and it still gives a nullPointerException, so guess it has something do do with the FindViewById(R.id.Player1name), but I don't know exactly what yet. I use different views for different screens using ViewPagerIndicator, could that have something to do with it?

Life_counterActivity.java see line no.72 – Samir Mangroliya May 26 '12 at 04:16 — Samir Mangroliya, May 26 '12 at 04:16

wattostudios · Answer 1 · 2012-05-28T13:24:17.277

See the Exception stack trace you posted - it says that the error was caused by: the line #72 in Life_counterActivity.java - this will give you some indication as to the objects that might be null.

Without knowing which line it actually is, it is probably one of the 6 lines that look like this...

((TextView)findViewById(R.id.Player1name)).setText(""+player1.name);

There are 2 possibilities...

The object player1 is null, so you can't ask for its name.
The R.id.Player1name can't be found - this is less likely, but you can't call setText() if it does actually return a null object.

Seeing as though its probably player1 or player2, could you please show where you're saving the Player object to the file - it looks like it might be creating the object from a file but not populating the variables. Assuming that Player implements Serializable, could you show the code of writeObject() and readObject() please. Refer to the Serializable java doc for info on these methods.

So, as a suggestion for your readObject() and writeObject() methods...

private void writeObject(ObjectOutputStream out) throws IOException{
    out.writeObject(name);
    out.writeInt(life);
    out.writeInt(totalWins);
    out.writeInt(totalLosses);
    out.writeObject(wins);
}
private void readObject(ObjectInputStream in) throws ClassNotFoundException, IOException{
    name = (String)in.readObject();
    life = in.readInt();
    totalWins = in.readInt();
    totalLosses = in.readInt();
    wins = (HashMap<String, Integer>) in.readObject();
}

ok, I added what you asked to the question, thanks for the help. — jjcard, May 28 '12 at 03:25
So, what I would suggest is that you write your own `readObject()` and `writeObject()` methods. I have edited my answer to include a suggested solution, which writes out each of the values, and reads them in again. I built this using the example shown in the summary at the top of the `ObjectInputStream` and `ObjectOutputStream` java docs. — wattostudios, May 28 '12 at 13:26
Thanks for the advice, but It still crashes at startup. I think I narrowed the issue down to it not being about the player object or player.name being null, but something do actually do with ((TextView)findViewById(R.id.Player1name)) — jjcard, Jun 23 '12 at 05:38

Android App crashes on startup while reading objects from java.lang.NullPointerException

1 Answers1