Very simple Graph implementation in Java

Solution.java

    private static class Vertex {
        private int uniqueLabel;

        public Vertex(int uniqueLabel) {
            super();
            this.uniqueLabel = uniqueLabel;
        }

        @Override
        public boolean equals(Object obj) {
            if (this == obj) return true;
            if (!(obj instanceof Vertex)) return false;

            Vertex _obj = (Vertex) obj;
            return _obj.uniqueLabel == uniqueLabel;
        }

        @Override
        public int hashCode() {
            return uniqueLabel;
        }

        public int getLabel() {
            return uniqueLabel;
        }

        public void setLabel(int uniqueLabel) {
            this.uniqueLabel = uniqueLabel;
        }
    }

    private static class Edge {
        private static final int DEFAULT_WEIGHT = 1;

        Vertex v1, v2;
        int weight;

        public Edge(Vertex v1, Vertex v2) {
            this(v1, v2, DEFAULT_WEIGHT);
        }

        public Edge(Vertex v1, Vertex v2, int weight) {
            super();
            this.v1 = v1;
            this.v2 = v2;
            this.weight = weight;
        }

        @Override
        public boolean equals(Object obj) {
            if (this == obj) return true;
            if (!(obj instanceof Edge)) return false;

            Edge _obj = (Edge) obj;
            return _obj.v1.equals(v1) && _obj.v2.equals(v2) &&
                   _obj.weight == weight;
        }

        @Override
        public int hashCode() {
            int result = v1.hashCode();
            result = 31 * result + v2.hashCode();
            result = 31 * result + weight;
            return result;
        }
    }

    private static class Graph {
        private Set<Vertex> vertices;
        private Set<Edge> edges;
        private Map<Vertex, Set<Edge>> adjList;

        public Graph() {
            vertices = new HashSet<>();
            edges = new HashSet<>();
            adjList = new HashMap<>();
        }

        public boolean addVertex(int label) {
            return vertices.add(new Vertex(label));
        }

        public boolean addVertex(Vertex v) {
            return vertices.add(v);
        }

        public boolean addVertices(Collection<Vertex> vertices) {
            return this.vertices.addAll(vertices);
        }

        public boolean removeVertex(int label) {
            return vertices.remove(new Vertex(label));
        }

        public boolean removeVertex(Vertex v) {
            return vertices.remove(v);
        }

        public boolean addEdge(Edge e) {
            if (!edges.add(e)) return false;

            adjList.putIfAbsent(e.v1, new HashSet<>());
            adjList.putIfAbsent(e.v2, new HashSet<>());

            adjList.get(e.v1).add(e);
            adjList.get(e.v2).add(e);

            return true;
        }

        public boolean addEdge(int vertexLabel1, int vertexLabel2) {
            return addEdge(new Edge(new Vertex(vertexLabel1),
                                    new Vertex(vertexLabel2)));
        }

        public boolean removeEdge(Edge e) {
            if (!edges.remove(e)) return false;
            Set<Edge> edgesOfV1 = adjList.get(e.v1);
            Set<Edge> edgesOfV2 = adjList.get(e.v2);

            if (edgesOfV1 != null) edgesOfV1.remove(e);
            if (edgesOfV2 != null) edgesOfV2.remove(e);

            return true;
        }

        public boolean removeEdge(int vertexLabel1, int vertexLabel2) {
            return removeEdge(new Edge(new Vertex(vertexLabel1),
                                       new Vertex(vertexLabel2)));
        }

        public Set<Vertex> getAdjVertices(Vertex v) {
            return adjList.get(v).stream()
                          .map(e -> e.v1.equals(v) ? e.v2 : e.v1)
                          .collect(Collectors.toSet());
        }

        public Set<Vertex> getVertices() {
            return Collections.unmodifiableSet(vertices);
        }

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

        public Map<Vertex, Set<Edge>> getAdjList() {
            return Collections.unmodifiableMap(adjList);
        }
    }

It is too small piece of code .