java - 货币实用程序 Java 错误代码 'int java.lang.Object.hashCode()'

Question

我正在尝试从 Java Util 货币显示我的货币对话框，但我在此处的简单试用项目中不断收到此错误，如何解决此问题以让我的对话框启动任何帮助将受到高度赞赏。 这是 GitHub 项目的帮助，我将非常感激。

货币助手类

class CurrencyHelper {

    private static final String[] MAIN_CURRENCIES = {"USD",
            "EUR", "GBP", "IRN", "AUD", "CAD", "SGD", "CHF", "MYR", "JPY", "CNY", "NZD","KSH"};
    private static final String CURRENCY_ISO    = "currency_iso";

    private static final DecimalFormat decimalFormatter = new DecimalFormat("#.00");


    @NonNull
    public static List<Currency> getMainAvailableCurrencies()
    {
        List<Currency> mainCurrencies = new ArrayList<>(MAIN_CURRENCIES.length);

        for(String currencyCode : MAIN_CURRENCIES)
        {
            try
            {
                Currency currency = Currency.getInstance(currencyCode);
                if( currency != null )
                {
                    mainCurrencies.add(currency);
                }
            }
            catch (Exception e)
            {
                Logger.getLogger("Unable to find currency with code: "+currencyCode);
            }
        }

        return mainCurrencies;
    }


    public static List<Currency> getOtherAvailableCurrencies()
    {
        List<Currency> mainCurrencies = getMainAvailableCurrencies();

        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT)
        {
            List<Currency> currencies = new ArrayList<>(Currency.getAvailableCurrencies());

            // Exclude main currencies
            Iterator<Currency> currencyIterator = currencies.iterator();
            while (currencyIterator.hasNext())
            {
                Currency currency = currencyIterator.next();

                if( mainCurrencies.contains(currency) )
                {
                    currencyIterator.remove();
                }
            }

            return currencies;
        }
        else
        {
            Set<Currency> currencySet = new HashSet<>();

            Locale[] locales = Locale.getAvailableLocales();
            for(Locale locale : locales)
            {
                try
                {
                    Currency currency = Currency.getInstance(locale);

                    if( mainCurrencies.contains(currency) )
                    {
                        continue; // Exclude main currencies
                    }

                    currencySet.add(currency);
                }
                catch(Exception ignored)
                {
                    // Locale not found
                }
            }

            List<Currency> currencies = new ArrayList<>(currencySet);
            Collections.sort(currencies, new Comparator<Currency>()
            {
                @Override
                public int compare(Currency lhs, Currency rhs)
                {
                    return lhs.getCurrencyCode().compareTo(rhs.getCurrencyCode());
                }
            });

            return currencies;
        }
    }

代码:

    public class Constants {

        private final static String SHARED_PREFERENCES_FILE_NAME = "currency_trial";

        private final SharedPreferences preferences;


        private Constants(@NonNull Context context) {
            preferences = context.getApplicationContext().getSharedPreferences(SHARED_PREFERENCES_FILE_NAME, Context.MODE_PRIVATE);
        }


        public void putInt(@NonNull String key, int value)
   {
            preferences.edit().putInt(key, value).apply();
        }

        public void putLong(@NonNull String key, long value)
        {
            preferences.edit().putLong(key, value).apply();
        }


        public void putString(@NonNull String key, @NonNull String value)
        {
            preferences.edit().putString(key, value).apply();
        }


        public void putBoolean(String key, boolean value)
        {
            preferences.edit().putBoolean(key, value).apply();
        }


        public int getInt(@NonNull String key, int defaultValue)
        {
            return preferences.getInt(key, defaultValue);
        }


        public long getLong(@NonNull String key, long defaultValue)
        {
            return preferences.getLong(key, defaultValue);
        }


        public boolean getBoolean(@NonNull String key, boolean defaultValue) {
            return preferences.getBoolean(key, defaultValue);
        }


        @Nullable
        public String getString(String key) {
            return preferences.getString(key, null);
        }


        private static Constants ourInstance;


        public static synchronized Constants getInstance(Context context) {
            if (ourInstance == null) {
                ourInstance = new Constants(context);
            }

            return ourInstance;
        }
    }


   [1]: https://github.com/annMusenya/Trial-Project

我的异步任务

  @SuppressLint("StaticFieldLeak")
    private void setupRecyclerView(final View v) {
        final RecyclerView recyclerView = v.findViewById(R.id.select_currency_recycler_view);
        recyclerView.setLayoutManager(new LinearLayoutManager(v.getContext()));


        new AsyncTask<Void, Void, Pair<SelectCurrencyAdapter, Integer>>()
        {
            @RequiresApi(api = Build.VERSION_CODES.KITKAT)
            @Override
            protected Pair<SelectCurrencyAdapter, Integer> doInBackground(Void... voids) {
                SelectCurrencyAdapter adapter = new SelectCurrencyAdapter(CurrencyHelper.getMainAvailableCurrencies(),
                        CurrencyHelper.getOtherAvailableCurrencies());
                return Pair.create(adapter, adapter.getSelectedCurrencyPosition(Objects.requireNonNull(getContext())));
            }

            @Override
            protected void onPostExecute(Pair<SelectCurrencyAdapter, Integer> data)
            {
                recyclerView.setAdapter(data.first);

                if( data.second > 1 )
                {
                    recyclerView.scrollToPosition(data.second-1);
                }
            }
        }.execute();
    }

完整错误代码:

2018-10-29 10:53:52.204 7840-8080/murray.ann.myapplication E/AndroidRuntime: FATAL EXCEPTION: AsyncTask #1
    Process: murray.ann.myapplication, PID: 7840
    java.lang.RuntimeException: An error occurred while executing doInBackground()
        at android.os.AsyncTask$3.done(AsyncTask.java:353)
        at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:383)
        at java.util.concurrent.FutureTask.setException(FutureTask.java:252)
        at java.util.concurrent.FutureTask.run(FutureTask.java:271)
        at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:245)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1162)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:636)
        at java.lang.Thread.run(Thread.java:764)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'int java.lang.Object.hashCode()' on a null object reference
        at java.util.concurrent.ConcurrentHashMap.get(ConcurrentHashMap.java:944)
        at java.util.Currency.getInstance(Currency.java:91)
        at murray.ann.myapplication.CurrencyHelper.getUserCurrency(CurrencyHelper.java:191)
        at murray.ann.myapplication.SelectCurrencyAdapter.getSelectedCurrencyPosition(SelectCurrencyAdapter.java:106)
        at murray.ann.myapplication.SelectCurrencyFragment$1.doInBackground(SelectCurrencyFragment.java:82)
        at murray.ann.myapplication.SelectCurrencyFragment$1.doInBackground(SelectCurrencyFragment.java:76)
        at android.os.AsyncTask$2.call(AsyncTask.java:333)

Answer 1

错误消息有时可能有点令人困惑。实际上错误并不在hashCode()方法中。实际上它尝试在空对象上调用此方法。

就您而言，这种情况发生在以下方法中:

static Currency getUserCurrency( Context context) {

    return Currency.getInstance(Constants.getInstance(context).getString(CURRENCY_ISO));
}

Constants.getInstance(context).getString(CURRENCY_ISO) 为空。