whats wrong with this code? It is not filtering the collection!!!

Question

public class CollectionsFilter {

    public static void main(String[] args) {
     List<Integer> list = Arrays.asList(new Integer[] { 1, 2, 3, 4, 5, 6, 7,
       8, 9, 10 });
     Collection<Integer> evenNumbers = Utils.filter(list,
       new Predicate<Integer>() {
        public boolean apply(Integer i) {
         if (i % 2 == 0) {
          return true;
         }
         return false;
        }
       });

     Collection<Integer> oddNumbers = Utils.filter(list,
       new Predicate<Integer>() {
        public boolean apply(Integer i) {
         if (i % 2 != 0) {
          return true;
         }
         return false;
        }
       });
     System.out.println("EVEN Numbers > " + evenNumbers);
     System.out.println("ODD Numbers > " + oddNumbers);
    }

}

where my Utils.filter() method is :

public static <T> Collection<T> filter(Collection<T> target,
      Predicate<T> predicate) {
     Collection<T> filteredCollection = new ArrayList<T>();
     for (T t : filteredCollection) {
      if (predicate.apply(t)) {
       filteredCollection.add(t);
      }
     }
     return filteredCollection;
    }

and the Prdicate:

public interface Predicate<T> {
    public boolean apply(T type);
}

Answer 1

That's because your Util.filter runs over empty filteredCollection which it creates in the beginning.

Answer 2

First of all, don't write this kind of code yourself. There's Google Collections for that.

Having said that: Try to iterate over target instead of over filteredCollection in your filter() method, that should fix it.