Gets the value of an instance field.

def get_field(self, state, field_name, field_type):
        """
        Gets the value of an instance field.
        """
        # get field reference
        field_ref = SimSootValue_InstanceFieldRef.get_ref(state=state,
                                                          obj_alloc_id=self.heap_alloc_id,
                                                          field_class_name=self.type,
                                                          field_name=field_name,
                                                          field_type=field_type)
        # load value from java memory
        return state.memory.load(field_ref, none_if_missing=True)