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Combo Box No Action

Posted by Rob Camick on May 17, 2009

A common GUI design principle is that the user should be able to use the keyboard or the mouse to achieve the same functionality. Because of this principle I’ve alway been a little puzzled about the default behaviour of a JComboBox. In particular the behaviour is different when using the mouse versus the keyboard when the popup is visible.

Use the mouse to click on the combo box to display the popup. Now try moving the mouse over the items in the popup menu and you will notice that the item becomes highlighted, but it does not become selected. That is, no events are fired and the value in the combo box display area does not change. To select an item and close the popup you must click on the item at which time an ActionEvent is fired.

Now try using the keyboard. Using the down arrow will cause the popup to display. Continue to move through the popup by using the down arrow. This time, not only are the items highlighted, but they also become selected. That is, an ActionEvent is fired and the combo box display area is changed to reflect the selection. The popup is then closed by using the enter key.

In most cases it probably doesn’t matter that the two behaviours are different. However, of the two behaviours I would consider the mouse behaviour to be more natural. Below are the problems I see with the default keyboard behaviour:

  • lack of escape functionality – the popup menu can easily be closed using the escape key. However, if you have used the arrow keys to navigate the popup then the original selection has already been lost. The only way to restore it to its original selected item is to find the item again and reselect it.
  • unnecessary overhead – you may be using the combo box to select an item in order to display additional information about that item. This information may come from a database. Querying a database for every selection may result in a sluggish GUI.

Now for the good news. If, like me, you don’t like (or want) the ActionEvent to fire when using the arrow keys it can easily be changed. Luckily for us a combo box can also be used as an editor in a JTable. In this case a property is set on the combo box so that the ActionEvent is only fired when the enter key is used. This tells the table to stop editing and save the selected item to the table model. We can use this property on a standalone combo box to achieve the same effect:

comboBox.putClientProperty("JComboBox.isTableCellEditor", Boolean.TRUE);

Try it out. Even if you don’t make this property the default behaviour its nice to know that it exists just in case you need it sometime.

Note, when using this property in JDK1.4.2 I noticed the the popup menu was not automatically closed when using the enter key. You had to manually close the popup in your ActionListener using code like the following:


The combo box closes automatically in JDK6 and I don’t know when the behaviour was changed.


3 Responses to “Combo Box No Action”

  1. Wolfgang said

    Hi Rob,

    at first, thank you for this great blog. It helped me a lot. Unfortunately I have the problem the other way round.
    I have a editable JComboBox in a JTable, it works great but I want the normal behaviour back.

    The normal behaviour of a combobox:
    While pushing the up/down button the selection is changed. By clicking TAB the focus is traversed to the next component.

    Within a JTable:
    The selection is not changed and by pressing TAB the combobox remains with the original selection and focuses the next cell.
    So you just have to hit enter to change the value.

    I tried to change this with the help of this article ( by sharing the action of the enter key. The selection is changed but now the focus traversal seems to be disabled. There is no chance to jump out of the cell by pressing tab.

    Just setting this property: comboBox.putClientProperty(“JComboBox.isTableCellEditor”, Boolean.FALSE);
    to false does not do the trick. Now it is impossible to just navigate through the list.

    Maybe you have an better advice for me?

    Best regards,

  2. Harshit said

    That’s very helpful Sir…i exactly needed my lot of time.
    Thank you :)

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