Custom Iterable, Issue with standard Interface?

Robert Klemme <>
Mon, 16 Oct 2006 16:35:01 +0200

I have a similar situation as demonstrated below. I cannot find a
proper solution to make method iterator() work properly. It works with
the custom interface Iterable2 (see below). I tried several
alternatives I could think of but to no avail (see comments in code).
Any other ideas? Or am I running into a limitation of Iterable?
Research did not turn up much useful information for this situation.
Thanks for any feedback!

Kind regards


package generics;

import java.util.HashSet;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
import java.util.Map.Entry;

// does not work because: The type WrappedTest cannot extend or
implement Iterable<? extends Map.Entry<K,V>>. A supertype may not
specify any wildcard
// public class WrappedTest<K, V> implements Iterable<? extends
Map.Entry<K, V>> {
public class WrappedTest<K, V> implements Iterable<Map.Entry<K, V>>,
Iterable2<Map.Entry<K, V>> {

     private static class En<Ke, Va> implements Map.Entry<Ke, Va> {

         public Ke getKey() {
             return null;

         public Va getValue() {
             return null;

         public Va setValue( Va value ) {
             return null;

     private Set<En<K, V>> set = new HashSet<En<K, V>>();
     // works but not usable:
     // private Set<Map.Entry<K, V>> set = new HashSet<Map.Entry<K,

     public Iterator<Map.Entry<K, V>> iterator() {
         // error in this line:
         return set.iterator();

     // this is ok
     public Iterator<? extends Entry<K, V>> iter() {
         return set.iterator();

     // works but inheritance from Iterable<Map.Entry<K, V>> fails:
// public Iterator<? extends Map.Entry<K, V>> iterator() {
// return set.iterator();
// }

package generics;

import java.util.Iterator;

public interface Iterable2<T> {

     public Iterator<? extends T> iter();


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