Gson and generic

GsonGeneric.java

package com.turlir.abakgists;

import com.google.gson.Gson;
import org.junit.Test;
import java.util.Objects;
import static org.junit.Assert.*;

public class Demo {

    @Test
    public void test() {
        ApiResponse<Model> mr = new ModelResponse(new Model("str", 5));
        mr.code = 5.5f;
        Gson gson = new Gson();
        String json = gson.toJson(mr);
        assertEquals("{\"payload\":{\"str\":\"str\",\"index\":5},\"code\":5.5}", json);

        ApiResponse<Model> resp = gson.fromJson(json, ModelResponse.class);
        assertEquals(mr, resp);
    }

    private static class ApiResponse<T> {
        T payload;
        float code;

        @Override
        public boolean equals(Object o) {
            if (this == o) return true;
            if (o == null || getClass() != o.getClass()) return false;
            ApiResponse<?> that = (ApiResponse<?>) o;
            return Float.compare(that.code, code) == 0 &&
                   Objects.equals(payload, that.payload);
        }

        @Override
        public int hashCode() {
            return Objects.hash(payload, code);
        }
    }

    private static class ModelResponse extends ApiResponse<Model> {

        ModelResponse(Model model) {
            payload = model;
        }
    }

    private static class Model {
        final String str;
        final int index;

        Model(String str, int index) {
            this.str = str;
            this.index = index;
        }

        @Override
        public boolean equals(Object o) {
            if (this == o) return true;
            if (o == null || getClass() != o.getClass()) return false;
            Model model = (Model) o;
            return index == model.index &&
                   Objects.equals(str, model.str);
        }

        @Override
        public int hashCode() {
            return Objects.hash(str, index);
        }
    }
}