FirstPageLoading.java

 class FirstPageLoading implements PartialStateChanges {
   
   @Override
   public HomeViewState computeNewState(HomeViewState previousState)
        return previousState.builder()
                .firstPageLoading(true)
                .firstPageError(null)
                .build();
    }
}

PartialStateChanges.java

interface PartialStateChanges {
   HomeViewState computeNewState(HomeViewState previousState)
}

PullToRefreshLoaded.java

class PullToRefreshLoaded implements PartialStateChanges {

  private final List<FeedItem> data;

  public PullToRefreshLoaded(List<FeedItem> data) {
    this.data = data;
  }

  @Override
  public HomeViewState computeNewState(HomeViewState previousState) {
        List<FeedItem> data = new ArrayList<>();
        data.addAll(this.data);
        data.addAll(previousState.getData());
        return previousState.builder()
                .pullToRefreshLoading(false)
                .pullToRefreshError(null)
                .data(data)
                .build();
    }
}

Reducer.java

private HomeViewState viewStateReducer(HomeViewState previousState, PartialStateChanges partialChanges) {
   return partialChanges.computeNewState(previousState);
}