Get the map keys and not the map values
<p>I have some data like this:</p>

<pre><code>Map&lt;Integer, String&gt; foo
</code></pre>

<p>Now I can get the corresponding <code>String</code> with <code>foo.get(1)</code></p>

<p>But is it also possible to get all the <code>Integer</code>s which have the <code>String</code> "abc"?</p>

<p>Like this pseudo code: <code>Integer[] someMore = foo.getKeys("abc")</code></p>
