public class MyGraph<V,E> extends SparseMultigraph<V,E>{
private ArrayList<MyNode> myNodeList;
public MyNode getNode(int nodeId){
myNodeList = new ArrayList<MyNode>();
myNodeList = (ArrayList<MyNode>)this.getVertices();
int i;
The following are the error msg:
Exception in thread "main" java.lang.ClassCastException: java.util.Collections$UnmodifiableCollection cannot be cast to java.util.ArrayList...
Can anyone help?
As other people have mentioned, ArrayList has a constructor that takes a collection of items, and adds all of them. Here's the documentation:
http://java.sun.com/javase/6/docs/api/java/util/ArrayList.html#ArrayList%28java.util.Collection%29
So you need to do:
ArrayList<MyNode> myNodeList = new ArrayList<MyNode>(this.getVertices());
However, in another comment you said that was giving you a compiler error. It looks like your class MyGraph is a generic class. And so getVertices() actually returns type V, not type myNode.
I think your code should look like this:
public V getNode(int nodeId){
ArrayList<V> myNodeList = new ArrayList<V>(this.getVertices());
return myNodeList(nodeId);
}
But, that said it's a very inefficient way to extract a node. What you might want to do is store the nodes in a binary tree, then when you get a request for the nth node, you do a binary search.
Try this code
Convert ArrayList to Collection
ArrayList<User> usersArrayList = new ArrayList<User>();
Collection<User> userCollection = new HashSet<User>(usersArrayList);
Convert Collection to ArrayList
Collection<User> userCollection = new HashSet<User>(usersArrayList);
List<User> userList = new ArrayList<User>(userCollection);
public <E> List<E> collectionToList(Collection<E> collection)
{
return (collection instanceof List) ? (List<E>) collection : new ArrayList<E>(collection);
}
Use the above method for converting the collection to list
The following code will fail:
List<String> will_fail = (List<String>)Collections.unmodifiableCollection(new ArrayList<String>());
This instead will work:
List<String> will_work = new ArrayList<String>(Collections.unmodifiableCollection(new ArrayList<String>()));
More information needed for a definitive answer, but this code
myNodeList = (ArrayList<MyNode>)this.getVertices();
will only work if this.getVertices() returns a (subtype of) List<MyNode>. If it is a different collection (like your Exception seems to indicate), you want to use
new ArrayList<MyNode>(this.getVertices())
This will work as long as a Collection type is returned by getVertices.
