Traverse through linked objects-CodePudding

I have this object, where each Rule stores a list of Rules:

public class Rule {

    private String name;
    private String condition;
    private List<String> result;
    private List<Rule> rules;
    private Map<String, List<String>> aliases = Maps.newHashMap();
    private boolean last = false;

}

What is the smartest and most efficient way to traverse through all the linked objects, and insert all the "results" field into a list, regardless the object on which they came from? eventually I'd like to have a list:

List<String> results containing all the results from all the objects.

I've been trying for hours and I'd appreciate your help. To get a list of all the objects themselves will also help me, like flatten the tree.

CodePudding user response：

You can use streams

Here is my recursive version for mapping list of rules to stream of results

  private Stream<String> mapToRules(List<Rule> rules) {
    return Stream.concat(rules.stream()
            .map(Rule::getResult)
            .flatMap(List::stream),
        rules.stream()
            .map(Rule::getRules)
            .flatMap(this::mapToRules));
  }

Version for a single root

  private Stream<String> mapToRules(Rule rule) {
    return Stream.concat(rule
            .getResult()
            .stream(),
        rule.getRules()
            .stream()
            .flatMap(this::mapToRules));
  }

You can then collect this stream to a list

mapToRules(list).collect(Collectors.toList());