public class Obligation {
    private String topic;
    private String status;
    private String comment;
    private String text;
}

public class ObligationStatus {

    private String topic;
    private String status;
    private String comment;
}

// this is what i have tried
        obList.stream().forEach(ob -> {
            osList.stream().forEach(os -> {
                if (ob.getTopic().equalsIgnoreCase(os.getTopic())) {
                    ob.setStatus(os.getStatus());
                    ob.setComment(os.getComment());
                }
            });
        });

// also tried to do this without using forEach, but compilation error here
        List<Obligation> result = obList.stream()
                .map(ob -> osList.stream().map(os -> os.getTopic().equals(ob.getTopic())).collect(Function.identity()))
                .collect(Collectors.toList());