Android NullPointerException when adding items to ArrayList<>

Question

I am stuck at this point and have no idea how to solve this NullPointerException... I did not change much but after the few code changes I had these problems and I now cannot figure where the error comes from... Code:

public class Levelhandler {
    public BoardElement[][] matrix;
    private int levelNr = 1;
    private ArrayList<Wall> allWalls;
    private ArrayList<Character> allCharacters;
    private ArrayList<Finish> allFinishes;

    // context
    private Context context;

    public Levelhandler(Context context) {
        this.context = context;
        matrix = new BoardElement[12][22];
        allWalls = new ArrayList<Wall>();
        Log.v("init", "done init");
        allCharacters = new ArrayList<Character>();
        allFinishes = new ArrayList<Finish>();

        for (int i = 0; i < 12; i++) {
            for (int j = 0; j < 22; j++) {
                matrix[i][j] = null;
            }
        }
    }

..........

public void loadWalls() {
        allWalls = null;
        Scanner s = null;

        try {
            s = new Scanner(context.getAssets().open(
                    "lev" + levelNr + "/walls.txt"));
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        ArrayList<String> list = new ArrayList<String>();
        while (s.hasNext()) {
            list.add(s.next());
        }
        s.close();
        for (String line : list) {
            allWalls.add(new Wall(context,
                    Integer.valueOf(line.split("\\;")[0]), Integer.valueOf(line
                            .split("\\;")[1])));
            matrix[Integer.valueOf(line.split("\\;")[0])][Integer.valueOf(line
                    .split("\\;")[1])] = new Wall(context, Integer.valueOf(line
                    .split("\\;")[0]), Integer.valueOf(line.split("\\;")[1]));
        }
    }

Error:

04-04 14:33:37.970: E/AndroidRuntime(10193): FATAL EXCEPTION: main
04-04 14:33:37.970: E/AndroidRuntime(10193): Process: com.paulk.pacman, PID: 10193
04-04 14:33:37.970: E/AndroidRuntime(10193): java.lang.NullPointerException
04-04 14:33:37.970: E/AndroidRuntime(10193):    at com.paulk.pacman.Levelhandler.loadCharacters(Levelhandler.java:121)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at com.paulk.pacman.PacManView.onDraw(PacManView.java:58)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.view.View.draw(View.java:15397)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.view.View.getDisplayList(View.java:14291)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.view.View.getDisplayList(View.java:14333)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.view.View.draw(View.java:15111)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.view.ViewGroup.drawChild(ViewGroup.java:3318)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.view.ViewGroup.dispatchDraw(ViewGroup.java:3155)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.view.View.getDisplayList(View.java:14286)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.view.View.getDisplayList(View.java:14333)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.view.View.draw(View.java:15111)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.view.ViewGroup.drawChild(ViewGroup.java:3318)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.view.ViewGroup.dispatchDraw(ViewGroup.java:3155)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.view.View.getDisplayList(View.java:14286)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.view.View.getDisplayList(View.java:14333)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.view.View.draw(View.java:15111)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.view.ViewGroup.drawChild(ViewGroup.java:3318)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.view.ViewGroup.dispatchDraw(ViewGroup.java:3155)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.view.View.getDisplayList(View.java:14286)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.view.View.getDisplayList(View.java:14333)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.view.View.draw(View.java:15111)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.view.ViewGroup.drawChild(ViewGroup.java:3318)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.view.ViewGroup.dispatchDraw(ViewGroup.java:3155)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.view.View.getDisplayList(View.java:14286)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.view.View.getDisplayList(View.java:14333)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.view.View.draw(View.java:15111)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.view.ViewGroup.drawChild(ViewGroup.java:3318)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.view.ViewGroup.dispatchDraw(ViewGroup.java:3155)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.view.View.getDisplayList(View.java:14286)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.view.View.getDisplayList(View.java:14333)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.view.View.draw(View.java:15111)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.view.ViewGroup.drawChild(ViewGroup.java:3318)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.view.ViewGroup.dispatchDraw(ViewGroup.java:3155)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.view.View.draw(View.java:15400)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.widget.FrameLayout.draw(FrameLayout.java:472)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at com.android.internal.policy.impl.PhoneWindow$DecorView.draw(PhoneWindow.java:2583)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.view.View.getDisplayList(View.java:14291)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.view.View.getDisplayList(View.java:14333)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.view.HardwareRenderer$GlRenderer.buildDisplayList(HardwareRenderer.java:1585)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.view.HardwareRenderer$GlRenderer.draw(HardwareRenderer.java:1457)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.view.ViewRootImpl.draw(ViewRootImpl.java:2779)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.view.ViewRootImpl.performDraw(ViewRootImpl.java:2645)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2213)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1256)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6635)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.view.Choreographer$CallbackRecord.run(Choreographer.java:813)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.view.Choreographer.doCallbacks(Choreographer.java:613)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.view.Choreographer.doFrame(Choreographer.java:583)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:799)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.os.Handler.handleCallback(Handler.java:733)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.os.Handler.dispatchMessage(Handler.java:95)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.os.Looper.loop(Looper.java:146)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at android.app.ActivityThread.main(ActivityThread.java:5593)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at java.lang.reflect.Method.invokeNative(Native Method)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at java.lang.reflect.Method.invoke(Method.java:515)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1283)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1099)
04-04 14:33:37.970: E/AndroidRuntime(10193):    at dalvik.system.NativeStart.main(Native Method)

The NPE is happening at loadCharacters, which you didn't post. — m0skit0, Apr 04 '15 at 12:49
The error message is telling you where the NullPointerException occurs. Did you try to debug the code? — Chetan Kinger, Apr 04 '15 at 12:49
@Paulomato, add your code in your question by editing your post. Not in a comment — Jibran Khan, Apr 04 '15 at 12:55

score 3 · Accepted Answer · edited Apr 04 '15 at 12:58

3

Just comment out this line allWalls = null; and add allWalls.clear();

edited Apr 04 '15 at 12:58

Hardik

17,179
2
35
40

answered Apr 04 '15 at 12:53

Patel Hiren

305
2
11

Thank yout soooooo much this works perfectly ;) – Paulomato Apr 04 '15 at 12:55
@Paulomato Learn to read stacktraces mate – m0skit0 Apr 04 '15 at 13:05
:P i will for next time – Paulomato Apr 04 '15 at 14:22

score 0 · Answer 2 · answered Apr 04 '15 at 12:57

In your loadWalls() method you make allWalls = null in an apparent attempt to clear the list. You then use allWalls.add(), which will throw the Exception as the variable is null

The correct way to do this is as follows:

public void loadWalls() {
    //clear current list
    allWalls.clear();
    //...rest of code
}

Android NullPointerException when adding items to ArrayList<>

2 Answers2