Using Generics in java

Hi,
I have the following code :

public static LatestFetchResponse parseFetchResponse(@Nullable String responseBody,@NotNull GsonBuilder jsonBuilder)
    {
        FetchBuddyMessagesResponse fetchBuddyChats = new FetchBuddyMessagesResponse();
        FetchGroupMessagesResponse fetchGroupChats = new FetchGroupMessagesResponse();
        ChatsFetchError fetchChatError = new ChatsFetchError();

        Gson gson = jsonBuilder.create();

        JsonParser jsonParser = new JsonParser();
        JsonElement object = jsonParser.parse(responseBody).getAsJsonObject();

        if (Utils.isFetchError(object))
        {
            fetchChatError = gson.fromJson(object, ChatsFetchError.class);
        }
        else
        {
            if (Utils.isBuddyChat(object))
            {
                fetchBuddyChats = gson.fromJson(object, FetchBuddyMessagesResponse.class);
            }
            else
            {
                fetchGroupChats = gson.fromJson(object, FetchGroupMessagesResponse.class);
            }
        }


        return new LatestFetchResponse(fetchBuddyChats, fetchGroupChats, fetchChatError);
    }

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The above code is repeated in many classes except the class name LatestFetchResponse gets changed.

How do i take it out and make it a generic function.

I tried something like :
public static <T> T parseFetchResponse(@Nullable String responseBody,@NotNull GsonBuilder jsonBuilder)
{
.
.
.
.
return return new T(fetchBuddyChats, fetchGroupChats, fetchChatError);

But this is giving error.

class FetchResult { FetchResult(FetchBuddyMessagesResponse fetchBuddyChats, FetchGroupMessagesResponse fetchGroupChats, ChatsFetchError fetchChatError) { } } class LatestFetchResult extends FetchResult { } class WhatEver<T extends FetchResult> { public static T parseFetchResponse(@Nullable String responseBody,@NotNull GsonBuilder jsonBuilder) { return new T(fetchBuddyChats, fetchGroupChats, fetchChatError); } }

LVL 39

ste5anSenior DeveloperCommented: 2015-03-02

This does not look like a case for a generic. Just normal inheritance. But: even then I don't understand you approach here. A kind of factory method?

As a generic, it must be constrained, thus your different fetch result classes must inherit from the same base class/interface providing your 3 parameter constructor.

E.g. something like this (air-code):

Using Generics in java

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