How to retrieve the size and clear a sesame repository using Java API

Question

Some functions of the openrdf-workbench for sesame 2.7 are really usefull.

• obtain repository's size
• clear the repository

How can someone do that using java API ?

for the reposirory size, is it necessary to use a sparql query

SELECT ?x ?y ?z WHERE { ?x ?y ?z }

and then count the resultSet. ?

and for clearing the repository, do SPARQ has clauses to delete triples ?

thanks