Need help porting some very terse Java code to Xojo

General Programming
1

I’m trying to port this Java tutorial to Xojo. I’m struggling to unpack the Set function below because, whilst short and elegant, it crams a lot of conversions into a small space and I’m not sure if I’m understanding it correctly:

public interface GraphNode {
    String getId();
}


public class Graph<T extends GraphNode> {
    private final Set<T> nodes;
    private final Map<String, Set<String>> connections;

    public T getNode(String id) {
        return nodes.stream()
            .filter(node -> node.getId().equals(id))
            .findFirst()
            .orElseThrow(() -> new IllegalArgumentException("No node found with ID"));
    }

    public Set<T> getConnections(T node) {
        return connections.get(node.getId()).stream()
            .map(this::getNode)
            .collect(Collectors.toSet());
    }
}

I basically can only figure what is happening up to the .stream() method call:

  1. Get the Id of the passed node GraphNode
  2. Get the Set<String> from the connections Map whose key matches the retrieved Id

What I don’t understand is what is happening here:

.map(this::getNode).collect(Collectors.toSet())

Can someone provide pseudocode to explain this?

2

not sure where stream comes from as it doesnt seem to be part of Set or Map …

3

Looks like it’s another interface that is essentially a glorified For...Each loop.

I actually stumbled across an article from May 2003 in xDev Magazine where Joe Strout has written a tutorial doing exactly what I was looking for (an A* pathfinding algorithm). I’ve decided to iterate on his example.