使用JComboBox从同一对象内的数据更改JLabel：

Question

I am trying to design a GUI, and I am really stuck on a certain issue, which involves using JComboBox to change data in a JLabel, but the catch is the data in the JLabel comes from object data the combo box needs.

Example: hypothetical arraylist with objects in each locale:

ArrayList<Animals> FarmAnimals = new ArrayList<Animals>();

FarmAnimals.add(new Animals("Cows", "Black"));    
FarmAnimals.add(new Animals("Pigs",  "Pink");    
FarmAnimals.add(new Animals("Sheep",  "White"));

Now, I want to populate the JComboBox with "Cows", "Pigs", and "Sheep", which is easily done with making a string array of the values. The problem is that, when I, hypothetically, select "Cows", I want a color JLabel to display "Black", "Pink", and "White" respectively when chosen: ideally from the object data within the array (just in case I have more data for Cows or whatever like paw size or loudness of animal noise that I'd like to input later).

Is there any way to get an ItemListener to do this, or at least is there a tutorial that shows how to directly influence JLabel data from objects associated with what's in the JComboBox? Or am I just being stupid and there's a much better way of doing it? Thanks.

This might be a better example:

http://pokemonshowdown.com/damagecalc/

Notice that when you change the EV's or the IV's, or if you change the pokemon, the stats on the side directly change with respect to the Pokemon chosen and the change in the EV & IV inputs. I want this behavior in the GUI I'm making (stats change directly based on inputs, which I assume are directly connected to object data stored for each Pokey.) but I can't seem to mimic it.

Answer 1

One technique here is:

• Store all your Animal data in an array, as you are currently doing.
• Give the Animal class a method to receive the relevant object data, in whatever form most naturally represents it (for example, if all your animal-specific data is a list of strings like colors, a String[] or a List<String> would be a good way to hold this data). Let's call this method getData() .
• Override Animal.toString() to return the name of the animal that you want to display in the combo box.
• Now, populate the combo box with a list of animals. Use JComboBox.addItem to add each Animal directly to the combo box.
• Add an action listener to the combo box. In the action listener, you may use (Animal)comboBox.getSelectedItem() to retrieve the selected Animal directly.
• Now that you have the selected Animal , you can call theAnimal.getData() to get the data you want to put in the label. You can call any other methods of Animal here too.

Basically, the idea above is to take advantage of JComboBox 's ability to directly store and return your actual objects. Then you can get the relevant data directly from the selected Animal , and update other GUI elements (eg your label) with that data accordingly.

A couple of things to note about the above:

• If overriding Animal.toString() to provide a display string is not appropriate for your situation for some reason (eg, as MadProgrammer points out in the comments, toString() is typically used for debugging output rather than information meaningful to a user), you have other options. You could, eg, add String s to the combo box and, if the combo box is not sorted, take advantage of the fact that the combo box indices are the same as the indices into your Animal array. Then in your action listener, you get the selected index, and look up the animal that way. Another option is to define a custom ListCellRenderer , which is beyond the scope of this answer (but information is readily available on the internet).
• You also may notice that you don't actually need the separate animal array with the above approach. You could just use the combo box itself as the "array". This may be sufficient for your needs, but bear in mind that it does tie your logic very closely to the GUI, and could cause problems in more complicated applications, especially when eg writing unit tests, or when writing methods that expect the collection of animals (and you end up having to pass the JComboBox / ComboBoxModel itself, or copy the items out of it into a temporary array), etc.

Sorry if that was a little vague, hopefully it gets you started down the right path.