Java convert Set<Set<String>> to List<List<String>>

Question

In Java I am having trouble converting from a Set<Set<String>> to a List<List<String>> and then populating this list with the contents of the Set<Set<String>>

Here is my code:

Set<Set<String>> treeComps = compExtractor.transform(forest); // fine
List<List<String>> components = new List<List<String>>();     // does not work
components.addAll(treeComps);                                 // does not work

Answer 1

You can't instantiate an instance of the List interface, you need to use one of the implementations like ArrayList. Then you can iterate over the outer set in treeComps, create a new ArrayList for each inner set, call addAll on this ArrayList and then add the list to components.

List<List<String>> components = new ArrayList<List<String>>();
for( Set<String> s : treeComps )
{
  List<String> inner = new ArrayList<String>();
  inner.addAll( s );
  components.add( inner );
}

Answer 2

I think only way is iterate over outer set. Get inner set and user new ArrayList<String>(innerSet)

Add above result list to outerlist.

Answer 3

Something like this...

Set<Set<String>> treeComps = compExtractor.transform(forest);
List<List<String>> lists = new ArrayList<List<String>>();
for (Set<String> singleSet : treeComps) {
    List<String> singleList = new ArrayList<String>();
    singleList.addAll(singleSet);
    lists.add(singleList);
}

Answer 4

List<List<String>> components = new Vector<List<String>>();
List<String> n;
for( Set<String> s : trerComps ) {
   n = new Vector<String>();
   n.addAll( s );
   components.add( n);
}