Using Java please help me complete these methods

import java.util.ArrayList; import java.util.Collection; import java.util.HashMap; import java.util.HashSet; import java.util.List; import java.util.Map; import java.util.Set; import java.util.stream.Collectors;

public class UndirectedGraph> extends Graph {

private Map> graph; /** do not change the constructor */ public UndirectedGraph() { this.graph = new HashMap<>(); } /** * @return true if graph is empty, false otherwise. */ public boolean isEmpty() { // TODO: Complete this method // Hint: An empty graph contains zero vertices return true; // this line needs to be rewritten }

/** * @return the size (i.e. number of vertices) of this graph */ public int getSize() { // TODO: compute the size return 0; // this line needs to be rewritten }}