praktikum-holons/src/holeg/model/Grid.java

package holeg.model;

import java.util.*;

public class Grid {
    private List<GridNode> nodes = new ArrayList<>();
    private Set<GridEdge> edges = new HashSet<>();
    private HashMap<GridNode, List<GridEdge>> edgesPerNode = new HashMap<>();

    public void addNode(GridNode node) {
        if (node == null)
            throw new IllegalArgumentException("node is null");
        nodes.add(node);
    }

    private void addEdgeToMap(GridNode node, GridEdge edge) {
        List<GridEdge> edges = edgesPerNode.getOrDefault(node, new ArrayList<>());
        edges.add(edge);
        edgesPerNode.put(node, edges);
    }

    public void addEdge(GridEdge edge) {
        if (edge == null)
            throw new IllegalArgumentException("edge is null");

        if (edges.contains(edge))
            return;
        edges.add(edge);

        addEdgeToMap(edge.getFrom(), edge);
        addEdgeToMap(edge.getTo(), edge);
    }

    public List<GridNode> getNodes() {
        return Collections.unmodifiableList(nodes);
    }

    public Set<GridEdge> getEdges() {
        return Collections.unmodifiableSet(edges);
    }

    public List<GridEdge> getEdges(GridNode node) {
        if (edgesPerNode.containsKey(node))
            return Collections.unmodifiableList(edgesPerNode.get(node));
        return Collections.emptyList();
    }
}