How to make it so that when you select an item in JComboBox, the list of items does not collapse. For example, in order to be able to select multiple elements.
JComboBox definitely not suitable for this. If you want the component to overlap the GUI part and not to be a combo box or
JMenu , then the window will be the only solution, as far as I know. If you want the list to appear in the window, but look and hide as a combo box, then there are such tools in SWT. The only thing you will then need to think about is which element of the list to display in such a combo box as selected after hiding the list, if several elements have been selected.
It is impossible, it is necessary