Re: iterator over superclass of collection

From:

Tom Hawtin <usenet@tackline.plus.com>

Newsgroups:

comp.lang.java.programmer

Date:

Tue, 17 Apr 2007 23:37:33 +0100

Message-ID:

<46254b6c$0$8752$ed2619ec@ptn-nntp-reader02.plus.net>

Frank Fredstone wrote:

I want to expose an iterator over a collection, where the iterator
returns elements that are a super class of the actual
objects. Essentially, so I can implement interfaces.

I guess you could just use Iterator<? extends Aye> and Iterable<?
extends Aye>.

    public Iterator<Aye> iterator() {
        return new Iterator<Aye>() {
            private Vector<? extends Aye> vec = ayes;
            private Iterator<? extends Aye> it = vec.iterator();
            public boolean hasNext() { return it.hasNext(); }
            public Aye next() { return it.next(); }
            public void remove() { it.remove(); }
        };
    }

This code needn't be so specific:

     public static <T> Iterator<T> iterator(
         Iterable<? extends T> iterable
     ) {
         final Iterable<? extends T> target = iterable.iterator();
         return new Iterator<T>() {
             public boolean hasNext() {
                 return target.hasNext();
             }
             public T next() {
                 return target.next();
             }
             public void remove() {
                 target.remove();
             }
         };
     }

Tom Hawtin