return readOnlyIterator;
      }

      @Override
      public Entry<E> next() {
        last = super.next();
        return last;
      }

      @Override
      public void remove() {
        checkState(last != null, "no calls to next() since the last call to remove()");
        ConcurrentHashMultiset.this.setCount(last.getElement(), 0);
        last = null;
      }

        AvlNode<E> next = current.succ();

        current.elemCount = 0;
        // Also clear these fields so that one deleted Entry doesn't retain all elements.
        current.left = null;
        current.right = null;
        current.pred = null;
        current.succ = null;

        current = next;
      }
      successor(header, header);

	// request to get next set of objects. Server lists objects in alphabetical
	// order Note: This element is returned only if you have delimiter request parameter
	// specified. If response does not include the NextMaker and it is truncated,
	// you can use the value of the last Key in the response as the marker in the
	// subsequent request to get the next set of object keys.

    assertEquals(expectedPermutation, permutations.next());
  }

  private <T> void assertNoMorePermutations(Iterator<List<T>> permutations) {
    assertFalse("Expected no more permutations, but there was one.", permutations.hasNext());
    try {
      permutations.next();
      fail("Expected NoSuchElementException.");
    } catch (NoSuchElementException expected) {
    }

    // ...and then putIfAbsent. Simulate failure on both
    when(backingMap.putIfAbsent(eq(KEY), isA(AtomicInteger.class))).thenReturn(existing);

    // next map.get()
    when(backingMap.get(KEY)).thenReturn(existingZero);
    // since get returned zero, try a replace; that fails due to a simulated race

import org.apache.lucene.queryparser.classic.ParseException;
import org.apache.lucene.queryparser.classic.QueryParser.Operator;
import org.apache.lucene.queryparser.ext.ExtendableQueryParser;
import org.apache.lucene.queryparser.ext.Extensions.Pair;
import org.apache.lucene.search.PhraseQuery;
import org.apache.lucene.search.Query;
import org.apache.lucene.search.TermQuery;
import org.codelibs.fess.Constants;

   * high 32 bits of each long is the "prev" pointer, whereas the low 32 bits is the "succ" pointer
   * (pointing to the next entry in the linked list). The pointers in [size(), entries.length) are
   * all "null" (UNSET).
   *
   * <p>A node with "prev" pointer equal to {@code ENDPOINT} is the first node in the linked list,
   * and a node with "next" pointer equal to {@code ENDPOINT} is the last node.
   */

    set("c", "c1", "c2")
    val iterator = cache.snapshots()
    assertThat(iterator.hasNext()).isTrue()
    iterator.next().use {
      assertThat(it.key()).isEqualTo("a")
      it.assertValue(0, "a1")
      it.assertValue(1, "a2")
    }
    assertThat(iterator.hasNext()).isTrue()
    iterator.next().use {
      assertThat(it.key()).isEqualTo("b")
      it.assertValue(0, "b1")
      it.assertValue(1, "b2")
    }

///

The only new thing is the `callbacks=invoices_callback_router.routes` as an argument to the *path operation decorator*. We'll see what that is next.

## Documenting the callback

The actual callback code will depend heavily on your own API app.

And it will probably vary a lot from one app to the next.

It could be just one or two lines of code, like:

```Python
callback_url = "https://example.com/api/v1/invoices/events/"

    return new AbstractIterator<E>() {
      @Override
      @CheckForNull
      protected E computeNext() {
        while (entries.hasNext()) {
          Entry<E, ?> entry = entries.next();
          if (targetNode.equals(entry.getValue())) {
            return entry.getKey();
          }
        }
        return endOfData();
      }
    };
  }

  @Override