Swimlane assignment through API?

[jmjava]

In the websale examples' process defintion swimlanes are set via assignment expressions:

<swimlane name="buyer" />

 <swimlane name="salesman">
 <assignment expression="user(ernie)" />
 </swimlane>

 <swimlane name="accountant">
 <assignment expression="user(bert)" />
 </swimlane>

 <swimlane name="shipper">
 <assignment expression="user(grover)" />
 </swimlane>

I am looking the Swimlane source and there are methods to set the ActorIdExpression and the PooledActorsExpression.

Is swimlane.setActorIdExpression("ernie") the same thing as the assignment expression above?

How can i achieve the same result as the XML code above in pure java?

-jm