@Override
public void actionPerformed(ActionEvent e) {
// open File chooser to select sub directory
JFileChooser fc = new JFileChooser();
// create files which can be choosen by the user
RelativeDirectoryFileFilter filter = new RelativeDirectoryFileFilter(
parentDirectory);
filter.setParentDirectoryTitle("Project");
fc.setFileFilter(filter);
filter = null;
fc.setFileSelectionMode(JFileChooser.DIRECTORIES_ONLY);
fc.setAcceptAllFileFilterUsed(false);
// set current directory to preoject directory