Question

I am trying to make a Graph class with generic vertices and adjacency lists and I am getting a generic array creation error at line 10 of the following code. Earlier I was getting the same error at line 11 but it was solved by casting. But this error remains. What is wrong in the code?

import java.util.HashSet;

public class Graph<T> {
    private int numVertices;
    private T[] vertex;
    private HashSet<T>[] adjacent;

    public Graph(int numVertices) {
            this.numVertices = numVertices;
            vertex = (T[]) new T[numVertices];
            adjacent = (HashSet<T>[]) new HashSet[numVertices];
    }
}

Answer 1

Don’t mix arrays with collections. Use just collections:

private List<HashSet<T>> adjacent;

You can then choose to use ArrayList as a List implementation. It’s same efficient and more flexible.