How to read a graph using Hashmap?

Question

I got a code from this site and when i try to run i'm getting error in the HashMap.what's wrong with this?do i need to import anything?

import java.util.*;

public class Graph {

    private HashMap<String, Vertex> myVertices;
    private HashMap<Vertex, TreeSet<Vertex>> myAdjList;
    private static final TreeSet<Vertex> EMPTY_SET = new TreeSet<Vertex>();
    public static final int INFINITY = Integer.MAX_VALUE;


}

Error is

Graph1.java:19: error: cannot find symbol
    private HashMap<String, Vertex> myVertices;
                            ^
  symbol:   class Vertex
  location: class Graph1
Graph1.java:24: error: cannot find symbol
    private HashMap<Vertex, TreeSet<Vertex>> myAdjList;