Retrieving leaderboards to display them in a custom view

GetLeaderboard.java

public abstract class GetLeaderboard{
    private static final int MAX_RESULTS = 25;
    
    /**
     * Check documentation for LeaderboardVariant to see possible values for timeSpan and collection
     */
    public void getTopScores(GoogleApiClient googleApiClient, String leaderboardID, int timeSpan, int collection) {
        PendingResult<Leaderboards.LoadScoresResult> pendingScores = Games.
                Leaderboards.loadTopScores(googleApiClient, leaderboardID,
                timeSpan, collection, MAX_RESULTS, true);
        processPendingResult(pendingScores);
    }
    
    /**
     * Check documentation for LeaderboardVariant to see possible values for timeSpan and collection
     */
    public void getPlayerCenteredScores(GoogleApiClient googleApiClient, String leaderboardID, int timeSpan, int collection) {
        PendingResult<Leaderboards.LoadScoresResult> pendingScores = Games.
                Leaderboards.loadPlayerCenteredScores(googleApiClient, leaderboardID,
                timeSpan, collection, MAX_RESULTS, true);
        processPendingResult(pendingScores);
    }

    protected void processPendingResult(PendingResult<Leaderboards.LoadScoresResult> pendingScores){
        pendingScores.setResultCallback(new ResultCallback<Leaderboards.LoadScoresResult>() {
            @Override
            public void onResult(Leaderboards.LoadScoresResult loadScoresResult) {
                List<LeaderboardScore> leaderboardScores = extractScores(loadScoresResult);
                notifyScoresLoaded(leaderboardScores);
            }
        });
    }

    protected List<LeaderboardScore> extractScores(Leaderboards.LoadScoresResult loadScoresResult) {
        LeaderboardScoreBuffer buffer = loadScoresResult.getScores();
        List<LeaderboardScore> leaderboardScores = new ArrayList<>();

        for(int i = 0; i < buffer.getCount(); i++){
            leaderboardScores.add(buffer.get(i));
        }
        return leaderboardScores;
    }
    
    public abstract void notifyScoresLoaded(List<LeaderboardScore> scoreList);
}