Himansu's answer is only true if the you are modifying the attributes of the objects passed as arguments but not the object reference itself.So, if you pass a Person instance for example and the process changes the 'name' property of the person you can still use the original person
you passed in the map.
But, if the process replaces the person with a new instance for example (this is always true for primitives data types and Strings), your original map is no longer valid. What you should (always) do is:
((WorkflowProcessInstance)processInstance).getVariable("hello");
Best Regards,