Question

I’m relatively new to Java and am used to generics in C# so have struggled a bit with this code. Basically I want a generic method for getting a stored Android preference by key and this code, albeit ugly, works for a Boolean but not an Integer, when it blows up with a ClassCastException. Can anyone tell me why this is wrong and maybe help me improve the whole routine (using wildcards?)?

    public static <T> T getPreference(Class<T> argType, String prefKey, T defaultValue,
        SharedPreferences sharedPreferences) {

    ...

    try {
        if (argType == Boolean.class) {
            Boolean def = (Boolean) defaultValue;
            return argType.cast(sharedPreferences.getBoolean(prefKey, def));
        } else if (argType == Integer.class) {
            Integer def = (Integer) defaultValue;
            return argType.cast(new Integer(sharedPreferences.getInt(prefKey, def)));
        } else {
            AppGlobal.logWarning("getPreference: Unknown type '%s' for preference '%s'. Returning default value.",
                    argType.getName(), prefKey);
            return defaultValue;
        }
    } catch (ClassCastException e) {
        AppGlobal.logError("Cast exception when reading pref %s. Using default value.", prefKey);
        return defaultValue;
    }
}

My calling code is:

        mAccuracy = GlobalPreferences.getPreference(Integer.class, prefKey, mAccuracy, sharedPreferences);

Here is the Android code for getInt():

public int getInt(String key, int defValue) {
        synchronized (this) {
            Integer v = (Integer)mMap.get(key);
            return v != null ? v : defValue;
        }
    }

I’ve tried various ways – using the native int, casting to an Integer, but nothing works.

Answer 1

It turns out the preference I’m trying to read is stored as a string so the cast exception is coming from inside the Android code not mine. Thanks for your help. But as I am a Java-newbie, if you think there is anything generally wrong with my routine, please teach me a better way.