OnFocus behavior of JFileChooser is unlike native File Dialog.
Steps to reproduce:
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1) Open a JFileChooser in WinLAF.
2) Select a file.
3) Take focus to some other window.
4) Take the focus back to FIleChooser.
5) Note that the focused color is on the file.
6) Now repeat the steps 1 to 4. You can use wordpad for opening the FileDilaog
7) Note that the focused color is on Look-in Combo. and the selected file color is non focused.
Please see the two images attached.