为什么方法getSelectedFile（）返回NULL

Question

JFileChooser.getSelectedFile()不起作用。当我尝试向变量分配此方法返回的值时，我得到了NullPointerException。怎么了？

chooseFile.addActionListener(new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    JFileChooser fileOpen = new JFileChooser("Choose file");
                    int res = fileOpen.showDialog(null, "Choose file");
                    if (res == fileOpen.APPROVE_OPTION) {
                        choosedFileOut = fileOpen.getSelectedFile();
                        System.out.println(fileOpen.getName());
                        if (fileOpen.getName() == null) {
                            System.out.println("selected file = null");
                        }
                    }
                }

            });