jpa - Assigning String as Google App Engine Entity Key -

i searched lot. still not able understand how assign string google app engine entity class id(key).

so have:

key id;

and

setid(string id) {      // know here can use id = keyfactory.createkey("","");  }

but don't know how use createkey method here assign string id. please consider user here entity class name.

p.s. using jpa.

thank you.

not sure of entity looking works me.,

@entity class person{     @id string personid;      string firstname; }

Babette