The Behaviour of Alt+O key is unlike native windows FileChooser
Steps to reproduce:
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1) Open SwingSet2 and Change the Look and feel to Windows.
2) Goto FileChooser Demo and Click on "Show Preview JFileChooser"
3) Select any image file and press Alt+O.
4) Now release Key O. You will that the image file is opened. Till you release the file does not open.
5) Now Open Wordpad.
6) Goto File--> Open.
7) Select any file to open.
8) Now press Alt + O.
9) Notice that as soon as u press alt+O key the files opens, no need to release the O key. This is unlike the Java implementation where file will be opened only when u release the O key.