java - 从列表中删除重复字符串时发生致命异常

Question

基本上，我的应用程序的一个函数应该从 Firestore 获取一个包含不同字符串的数组。然后另一个函数应该从该数组中选择 3 个不同的字符串并将其存储在列表中。字符串不应该相同，因此最终列表应该有 3 个唯一的随机字符串，这些字符串来 self 从 Firestore 获得的数组。

为了实现这一点，我有下面的代码(不幸的是我不是自己写的)。大多数情况下，这段代码工作正常，但有时我没有得到任何值(value)。正如我所说，有时我会收到此错误，这将我指向 removeDuplicates 方法:

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.android.guessit, PID: 30272
    java.lang.IndexOutOfBoundsException: Index: 2, Size: 2
        at java.util.ArrayList.get(ArrayList.java:437)
        at com.example.android.guessit.GameFlow.SecondRound.FragmentCategory_2.removeDuplicates(FragmentCategory_2.java:767)
        at com.example.android.guessit.GameFlow.SecondRound.FragmentCategory_2.access$100(FragmentCategory_2.java:49)
        at com.example.android.guessit.GameFlow.SecondRound.FragmentCategory_2$1.onComplete(FragmentCategory_2.java:99)
        at com.google.android.gms.tasks.zzj.run(Unknown Source:4)
        at android.os.Handler.handleCallback(Handler.java:873)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:214)
        at android.app.ActivityThread.main(ActivityThread.java:7050)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:494)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:965)

这是我使用我解释的函数的 fragment 。因此，基本上，getRandomElement 函数从我从数据库获取的数组中获取随机字符串并将其放入列表中，但在此之前，removeDuplicates 函数检查该字符串是否已经存在是否在列表中，并相应地删除它:

 @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {

...

        btnNavFragCat1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

                questionKeyRef.document(mTvCat1).get().addOnCompleteListener(new OnCompleteListener<DocumentSnapshot>() {
                    @Override
                    public void onComplete(@NonNull Task<DocumentSnapshot> task) {
                        if (task.isSuccessful()) {

                            DocumentSnapshot document = task.getResult();
                            List<String> questions = (List<String>) document.get("questions");

                            List<String> randomList = getRandomElement(questions, 6);

                            removeDuplicates(randomList);

                            viewModel.setCategory(mTvCat1);

                            category.put("category", mTvCat1);
                            setUpCategory();

                            setUpQuestions();
                        }
                    }
                });

            }
        });

...

    private void removeDuplicates(List<String> list) {
        int count = list.size();
        for (int i = 0; i < count; i++) {
            for (int j = i + 1; j < count; j++) {
                if (list.get(i).equals(list.get(j))) {
                    list.remove(j--);
                    count--;
                }
            }
        }

        query1 = list.get(0);
        query2 = list.get(1);
        query3 = list.get(2);

        Log.d("One", list.get(0));
        Log.d("Two", list.get(1));
        Log.d("Three", list.get(2));
    }

    private List<String> getRandomElement(List<String> list, int totalItems) {
        Random rand = new Random();
        List<String> newList = new ArrayList<>();
        for (int i = 0; i < totalItems; i++) {
            int randomIndex = rand.nextInt(list.size());
            newList.add(list.get(randomIndex));
        }
        return newList;
    }

...

我非常感谢任何帮助，并希望有人可以向我解释错误，并可能给我一个解决方案。

Answer 1

您应该在 RemoveDuplicates 中添加一些内容来避免 IndexOutOfBoundException:

private void removeDuplicates(List<String> list) {
    int count = list.size();
    for (int i = 0; i < count; i++) {
        for (int j = i + 1; j < count; j++) {
            if (list.get(i).equals(list.get(j))) {
                list.remove(j--);
                count--;
            }
        }
    }

    query1 = list.get(0);
    query2 = list.get(1);    //This
    query3 = list.get(2);    //And this, could be out of bound, for example if the list is something like {"a","a","a","a"}, so without duplicates it becomes {"a"}

    Log.d("One", list.get(0));
    Log.d("Two", list.get(1));
    Log.d("Three", list.get(2));
}

所以我建议改变它:

private void removeDuplicates(List<String> list) {
        int count = list.size();
        for (int i = 0; i < count; i++) {
            for (int j = i + 1; j < count; j++) {
                if (list.get(i).equals(list.get(j))) {
                    list.remove(j--);
                    count--;
                }
            }
        }
        count = list.size();

        if (count >= 3) {
            query1 = list.get(0);
            query2 = list.get(1);
            query3 = list.get(2);
        }
        else if (count >= 2) {
            query1 = list.get(0);
            query2 = list.get(1);
            query3 = "";
        }
        else if (count >= 1) {
            query1 = list.get(0);
            query2 = "";
            query3 = "";
        }
        else {
            query1 = "";
            query2 = "";
            query3 = "";
        }



        Log.d("One", query1);
        Log.d("Two", query2);
        Log.d("Three", query3);
    }