extract sublist of concrect product from a list of abstract product

Question

I construct an Hyper graph using jung library

  Hypergraph hypergraph = new SetHyperGraph<Vertex,HyperEdge>();

then I add all my vertex (image , tag , location)

    hypergraph.addVertex()

    ArrayList<Vertex> allVertex = hypergraph.getVertices;

Now I would to extract only image Vertex from my listallVertex

why this instruction is illegal?

    ArrayList<ImageVertex> allImageList=allVertex.subList(0,j);

Does Anyone have another solution?

Answer 1

Just a sample code

List<ImageVertex> allImageList = new ArrayList<ImageVertex>();
for (Vertex vertex : allVertex) {
  if (vertex instanceof ImageVertex) {
    allImageList.add((ImageVertex) vertex);
  }
}

Answer 2

Because ArrayList<ImageVertex> is not a subtype of ArrayList<Vertex>.

possible solution will be :

ArrayList<ImageVertex> allImageList= new ArrayList<>();

for (Vertex vertex: allVertex.sublist(0,j)) {
    if (vertex instanceof ImageVertex) {
        allImageList.add((ImageVertex) vertex);
    }
}