import java.io.File;
import javax.swing.JFileChooser;
public class Main {
public static void main(String[] args) {
final JFileChooser chooser = new JFileChooser(new File(".")) {
public void approveSelection() {
if (getSelectedFile().exists()) {
super.approveSelection();
} else
System.out.println("File doesn't exist");
}
};
chooser.addActionListener(e -> System.out.println(e));
chooser.setSelectedFile(new File("something.txt"));
int returnVal = chooser.showSaveDialog(null);
if (returnVal == JFileChooser.APPROVE_OPTION) {
System.out.println(chooser.getSelectedFile());
}
}
}