Those are streams on views on the map. My complaint is that a reader seeing &quot;maps don&#x27;t support streams&quot; with no further explanation is unlikely to get the correct idea, and may infer that something like<p><pre><code>  map.entrySet().stream().filter(e -&gt; e.getKey().equals(e.getValue())).findAny()
</code></pre>
is not expressible.