title: Java 8: how to 'JOIN' two Maps having the same Keys?
body: <p>I have two Maps, both sharing the same keys, .</p>
  
  <pre><code>Map&lt;Long/*JOIN.ID*/, Long/*Temp ID*/&gt; tempIDsMap;
  Map&lt;Long/*JOIN.ID*/, Long/*Real ID*/&gt; realIDsMap;
  </code></pre>
  
  <p>What I want to get (maybe using Java 8 Stream API and avoiding loops) is the JOIN of these maps on the <code>JOIN.ID</code> keys, to get a new Map like below:</p>
  
  <pre><code>Map&lt;Long/*Temp ID*/. Long/*Real ID*/&gt; realIDsByTempMap;
  </code></pre>