lLast">
<div class="block">An index backed by a <a href="http://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ConcurrentHashMap.html?is-external=true" title="class or interface in java.util.concurrent" class="externalLink"><code>ConcurrentHashMap</code></a>, which can be more efficient than <a href="../../index/hash/HashIndex.html" title="class in com.googlecode.cqengine.index.hash"><code>HashIndex</code></a> when used with
 (and only with) attributes which uniquely identify objects (primary key-ty