Generic class, can't return generic value

Question

I'm trying to deserialize a time string to a Joda DateTime, so I defined this deserializer:

public class JsonTimeDeserializer<T extends DateTime> implements JsonDeserializer<T> {
    @Override
    public T deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
        DateTimeFormatter dtf = DateTimeFormat.forPattern("HH:mm");
        return json == null ? null : dtf.parseDateTime(json.getAsString());
    }
}

I'm getting:

required: T
Found org.joda.time.DateTime

I don't understand. T extends DateTime.

What am I doing wrong?

Thanks

What makes you think that `T == DateTime` given that literally a line above you declared that `T extends DateTime`. In fact, why is this even generic? — Boris the Spider, Nov 04 '17 at 00:09

score 2 · Answer 1 · answered Nov 04 '17 at 00:26

Your first line should read

public class JsonTimeDeserializer implements JsonDeserializer<DateTime>

You don't need to create your own variable, just reference the existing one

When you extend a generic type and add a new type variable, you are making your type generic as well, which is not what you want in this case.

Generic class, can't return generic value

1 Answers1