[Demonstration 1]

[Buggy Method]
public boolean createDataFiles() {
    boolean exists = false;
    try {
        if (!cards.exists())
            cards.createNewFile();
    } catch (IOException e) {
        System.out.println("Problem creating file.");
    }
    exists = checkIfFilesExist();
    return exists;
}

[Buggy Hunk]
if (!cards.exists())

[Patch]
if (!cards.isFile())

[Demonstration 2]

[Buggy Method]
private void initData() {
    File path = Environment.getExternalStorageDirectory().getAbsoluteFile();
    Observable.from(path.listFiles()).flatMap(new Func1<File, Observable<File>>() {

        @Override
        public Observable<File> call(File file) {
            return Observable.from(file.listFiles());
        }
    }).filter(new Func1<File, Boolean>() {

        @Override
        public Boolean call(File file) {
            return file.getName().endsWith(".png") || file.getName().endsWith(".jpg");
        }
    }).map(new Func1<File, Bitmap>() {

        @Override
        public Bitmap call(File file) {
            return BitmapFactory.decodeFile(file.getAbsolutePath());
        }
    }).subscribeOn(Schedulers.io()).observeOn(AndroidSchedulers.mainThread()).subscribe(new Action1<Bitmap>() {

        @Override
        public void call(Bitmap bitmap) {
            final ImageView imageView = new ImageView(ImageActivity.this);
            imageView.setImageBitmap(bitmap);
            llRootBox.addView(imageView);
        }
    });
}

[Buggy Hunk]
return Observable.from(file.listFiles());

[Patch]
return file.listFiles()==null?null: Observable.from(file.listFiles());

[Demonstration 3]

[Buggy Method]
public static void main(String[] args) {
    try (JavaSparkContext jsc = Spark.newApp("MMDS Wiki").context();
        FileSystem fs = FileSystem.getLocal()) {
        Edits training = new Edits(jsc, "C:/Users/Marianne/Documents/Uni/HPI/Semester_1/MMDS-Mining_Massive_Datasets/data/test", fs);
        Recommender recommender = LDARecommender.load(sc, "C:/Users/Marianne/Documents/Uni/HPI/Semester_1/MMDS-Mining_Massive_Datasets/data/model");
        File file = new File("C:/Users/Marianne/Documents/Uni/HPI/Semester_1/MMDS-Mining_Massive_Datasets/data/eval-output");
        try (FileOutputStream out = new FileOutputStream(file)) {
            Evaluator eval = new Evaluator(recommender, training, "C:/Users/Marianne/Documents/Uni/HPI/Semester_1/MMDS-Mining_Massive_Datasets/data/ground_truth", out, fs);
            eval.evaluate(200, 100);
        }
    } catch (IOException e) {
        e.printStackTrace();
    }
}

[Buggy Hunk]
.load(sc, "C:/Users/Marianne/Documents/Uni/HPI/Semester_1/MMDS-Mining_Massive_Datasets/data/model");

[Patch]
.load(jsc.sc(), "C:/Users/Marianne/Documents/Uni/HPI/Semester_1/MMDS-Mining_Massive_Datasets/data/model");