Swing Jcombobox将第一个元素设置为默认选中

    String[] bookArray={"a","b","c"};
    JComboBox bookComboBox = new JComboBox(bookArray);
    bookComboBox.setSelectedIndex(0);
    bookComboBox.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            JComboBox cb= (JComboBox) e.getSource();
            bookNameSelected=(String) cb.getSelectedItem();
            System.out.println("book name selected:"+bookNameSelected);
            }
    });
    String[] bookArray={"a","b","c"};
    JComb