Re: Polymorfic Collection construction

"Oliver Wong" <>
Fri, 28 Apr 2006 20:30:23 GMT
<> wrote in message

Hello. I want to implement a method for filtering a class:

public Collection filter(Collection c) {

   Collection filteredCollection = "An object of the same class that

   for(Object obj : c) {

   return filteredCollection;

As you see, I want to get any kind of Collection and create a new
collection (of the same type that the first one). How can I do that?

    You could cop out and ask the user to provide you with the instance of
collection to populate.

<code tested="false">
public <T extends Collection> T filter(T collectionToReadFrom, T
collectionToPopulate) {
  /*Weird things happen if collectionToReadFrom == collectionToPopulate*/
  for(Object obj : collectionToReadFrom) {
    if(satisfiesSomeCondition(obj)) {
  return collectionToPopulate;


ArrayList input = /*whatever*/;
ArrayList output = filter(input, new ArrayList());

    - Oliver

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