well, severity and priority are enumerations.. so you can get the list from
(See my sample code at post 3 of https://jazz.net/forum/questions/94776/assertionfailedexception-problem-with-getting-the-values-of-attributes)
                           
                                    List<ILiteral> enumerationLiterals = enumeration
                                            .getEnumerationLiterals();

you have to get the states list from the WorkflowInfo object

here is some code from an advisor plugin
<code>
                // get the worker objects
                IAuditableCommon iac = ((ISaveParameter) data).getSaveOperationParameter().getAuditableCommon();
                WorkflowManager wfm = new WorkflowManager(iac);
               
                // reference the right object type (cast)
                IWorkItem workItem = (IWorkItem) auditable;
                // get the workflow this workitem is in, so we can get the labels of the states
                IWorkflowInfo x =wfm.getWorkflowInfo(workItem, monitor);

                if(Debug) System.out.println("the workitem state is "+ workItem.getState2().getStringIdentifier()+ "=" +x.getStateName(workItem.getState2()) );
                // if this workitem is going into resolved state (we accessed 'proposed new' state above
                if(x.getStateName(workItem.getState2()).equalsIgnoreCase(ResolvedState))
</code>

>i want only one method for retrieve the values

sorry, RTC doesn't not provide a data neutral single method.