The OWL API (http://owlapi.sourceforge.net/) is an ontology API to manage OWL 2 ontologies in Java applications and provides a high-level way to interact with DL reasoners. It can be considered as a de facto standard, as the most recent versions of the DL reasoners use OWL API to load and process the ontologies.
Jena is an ontology API to manage OWL ontologies and handle RDF data in Java applications, but support for OWL 2 is not available yet. Jena reasoners are based on answering queries over RDF graphs.
Although Jena cannot be directly imported into an Android project, there exist a project called Androjena (https://code.google.com/p/androjena) to port it to the Android platform. The last version of Androjena 0.5, which was used in our tests, contains all the original code of Jena 2.6.2.