Example of how an adapter collection could work in commons collections

CollectionUtils.java

/*
 * Creates an adapter collection of the given collection. The returned collection is an unmodifiable
 * view of {@code col}. Adapters will be created on the fly. In other words, when an element from col
 * is requested, it is passed to {@code transformer} and the result is returned. The created adapters
 * are not cached. If an element is requested twice, a new adapter will be created for each call.
 * 
 * @param col the collection to create the adapter collection for
 * @param transformer the tranformer that creates adapters from the elements of col
 * @param E the type of the elements in col
 * @param A the type of the adapters
 */
public static <A, E> Collection<A> adapterCollection(Collection<E> col, Transformer<A, E> transformer){
// what ever is necessary to do the trick...
}

Container.java

public class Container {
 
 private Collection<Containment> containments = new ArrayList()<Containment>;
 
 public Collection<Containment> getContainments() {
   return containments;
 }
 
}

ContainerAdapter.java

public class ContainerAdapter {
 
 private Container container;
 
 public ContainerAdapter(Container adaptee) {
   container = adaptee;
 }
 
 public Collection<ContainmentAdapter> getContainments() {
   return CollectionUtils.adapterCollection(container.getContainments, new Transformer<ContainmentAdapter, Containment>() {
     
     @Override
     public ContainmentAdapter transform(Containment containment) {
       return new ContainmentAdapter(containment);
     }
   }
 }
}