Well, that is not strictly true.  You can use neo4j embedded within Java:
<a href="http:&#x2F;&#x2F;neo4j.com&#x2F;docs&#x2F;stable&#x2F;tutorials-java-embedded.html" rel="nofollow">http:&#x2F;&#x2F;neo4j.com&#x2F;docs&#x2F;stable&#x2F;tutorials-java-embedded.html</a>