using abstract DAO factory

[Hanna Habashy]

hi all:
if abstract DAO factory frame work is used in a multi- threaded J2EE project, when is it appropriate to cach a single object and return it over and over again, vs. retruning a brand new object.
for example:
//cached object
abstract DAOFactory
{
privte EmployeeDAO MyEmployeeDAO = new EmplyeeDAO();
public EmplyeeDAO getEmplyeeDAO();
{ return MyEmployeeDAO;}
}
vs.
//new object
abstract DAOFactory
{
public EmplyeeDAO getEmpoyeeDAO()
{ return new EmplyeeDAO();}
}
I really appreciate it if someone can explain to me in what situation should I use which technique, and if there is any performance implication in using any of them.
thanks