For generic Swing elements like JComboBox, you can enter the type parameters in the "Code" tab after selecting the element.

There are some issues here:

1. You don´t know the format in which the type parameters have to be entered.
  I needed some time to find out (via web search) that you have to enter "<Integer>", whereas I expected it to accept "Integer".

2. Instead of a "free text" field, this feature should know about the required parameters and their structure (amount, restriction to be of special subtype etc.). The user should only be able to select correct parameters.

I think the availability of the "Type parameter" option implies an "intelligent" type parameter setter, instead of something only appending the entered text to the class name.

So the least necessary change would be to name the expected format in the description of the "Type Parameters" field, solving no. 1. Better, though, would be to make it safe in usage by implementing no. 2.

Thank you for considering this suggestion!