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The client property uses something like a hashmap. Look at the API doc for that class.
The key is what you give to a hashmap for it to return the value.

Your class provides get/set methods for storing values for each item in the list.

Your solution has no overlap with mine. See the JComponent class's ClientProperty methods.
For example:
final String TheKey = "A KEY";
JComboBox jcb1 = new JComboBox(...);...

You could put the value you want returned when a item is selected in the item itself.
See the ClientProperty methods for JComponent. Its frontends a hash map where you can store any value you want...